Maybe I am wrong but I have the impression that for some time now (a decade at least) there has been an ever increasing dislike for complexity and calls for ever simpler "rules light" systems.
Well, that little bit of pretense and calling what other designers and players do 'badwrongfun' in technical language goes back nearly two decades, but the movement away from complexity has been going on for nearly thirty years now.
So, a bit of background. In the 80's, design in RPGs was wide open and we barely had language to talk about the issues of design. There was a lot of good design and a lot of bad design, but one very common complaint about D&D is that the design was bad because it wasn't 'realistic', and there was a general sense in much of the community that many if not all of the problems tables encountered in a game was do to a lack of 'realism'. Various systems of Traveller and GURPS might also be worth looking at, and a trip into the world of GULLIVER (a modification of GURPS) would also be worthwhile. This led to a fetishization of realism as a goal of game design, which can be seen in extremely complex games of the period - HERO, and Rolemaster might be a very good examples, though the pain points in that complexity come up at different points. Since the goal of RPGs started out as basically 'Simulation of the World', the attributes of a system which were considered very admirable in a system were that it would be universal (able to simulate everything) and realistic (able to produce a simulation that produced intuitive or 'correct' results).
In the early '90's, the difficulties of play with super-realistic systems and the fact that realism hadn't in fact solved all table issues, and indeed created some, combined with a second thrust of design that could be seen in games like Pendragon and Ars Magica, led to backing away from realism as the primary goal of design, and with that a backing away from the super-complex designs.
In the late 90's and early 00's, a forum called 'The Forge' began some very formal and highly influential discussions on the design of RPGs. I personally feel almost all of their conclusions were wrong and the community ultimately became very unhealthy, but it was very helpful in some ways because it began attacking the problem of RPG design in a rigorous way using a lot of technical language and often from perspectives that had never really been clearly voiced before. This was the so called 'Indy' RPG movement, and almost any buzzword that you'll hear in RPG design like 'rules light' or 'story first' or 'fail forward' comes out of those discussions. Most of it is, as I said, just a load of horse hockey pucks, but it's worth studying in the same way bad philosophy is worth studying to make you think. A few very good designs came out of that, probably the best of which is 'Dogs in the Vineyard', which is sort of a 'Rules Light' game and a good example of what you can do with one.
Ultimately, I think this 'hate' for complexity is similar to the hate of classes and hit points that you saw from certain sectors in the 80's, where champions of 'realism' would sneer at the design of D&D because it lacked 'realism' and classes and hit points were considered proof if D&D's inferior design. This sneering was in fact mostly honored only in the breech, in that most of the games out there people were actually playing still featured classes and hit points in some form or the other, if often disguised by different terminology. And certainly out in the world of computer games where complexity could be dealt with without the bookkeeping overhead that plagued it in table top games, designers were still most frequently reaching for hit points and classes to solve design problems. The realism movement had some influences on the larger design of games, but it never was the cure all solution some trumpeted it as.
The same is true of the ideas that were championed by the 'Indy' movement. Almost no one plays those games compared to very complex traditional games like 3.X and Pathfinder. The 'Indy' games have influenced design of popular games in various ways, and there has been a lot of buzzwords thrown around in a marketing sort of way but 'Rules Light' has some major issues.
One big problem a 'Rules Light' game has is simply financial. It's pretty much impossible to have a major 'Rules Light' success because most rules light games are supposed to have all the rules contained in a single usually short supplement. It's hard to make money off of that, and if your game is a success, then how do you capitalize on it? It's easy to capitalize on the success of a 'Rules Heavy' game simply by issuing more supplements and more subsystems but if you try to do that for a 'Rules Light' game then it very quickly becomes something other than 'Rules Light' (usually 'rules medium'). This is why I say somewhat tongue in cheek that, "There is no such thing as a successful Rules Light RPG". This evolution can I think be seen in various games run off the FUDGE engine, then later the FATE engine, then later various FATE + stuff extensions. The more successful the game the more complex it tends to be.
There are also a lot of 'Rules Light' games that are anything but. For example, the game Mouse Guard which you might nominally think of as a rules light game has something like 11 different factors that can modify an individual die roll, and that modification to the roll can happen in 3 different ways. The results are every bit as fiddly as D&D at its worst.
I have similar issues with a lot of Indy inspired ideas like 'story first', which I think if you examine its implementation, has to be the most misleading claim in RPG history in the sense that if you examine the process of play, most of the mechanics designed to implement that tend to put the rules first and the story second to an even greater extent than old school D&D play. They are implementing some interesting ideas, but maybe not the ones they think they are implementing. (I should probably write a long post on that since its been knocking around in my head ever since I made attempts to play Mouseguard.)
I wonder where this hate for complexity comes from? Was it always there? Have people grown up, gotten jobs and dont have time/interest to learn rules anymore? Do they feel rules are constricting or that the granularity complex rules add like characters being differently competent in different skills instead of having one modifier for everything doesn't add anything to the game?
So, there is one area where complexity is I think pretty much dead, but its not RPGs. Back in the day, there were simulation games like Star Fleet Battles and Car Wars which I played, that if you go back and read now are very much revealed to be pieces of computer software that run on a human brain. I think there is probably very little interest in games like that any more simply because you can achieve the same and even more engaging results by playing them out actually on a computer. The Hex tile war game at least at the level of complexity of some of the older monstrosities isn't completely dead, because grognards, but it doesn't hold nearly the place in nerddom that it once had. But RPGs are still somewhat immune to this because even something like Skyrim or Witcher III can't begin to hope to simulate a GM, and we are probably decades away (at least) from having computer RPGs that can generate content and simulate free and open interaction in the way a good GM can.
Complexity in RPGs is far from dead. 5e is somewhat more streamlined than 3e and requires somewhat less bloat than the 4e design, but it's hardly by any stretch a 'Rules Light' game. It's more organized in its layout than 1e, but its probably at least as complicated as 1e and more complicated than 2e D&D and it takes a lot of inspiration from the 3e and 4e designs. If you look at what people are actually playing, almost all of it is at minimum 'rules medium' and most of it is 'rules heavy'.
And I agree with Morrus's comment from earlier, that the thing a 'rules light' RPG does very well is a quick one shot. I don't believe that they well support long sustained play that is the hallmark of most tabletop RPGs very well if at all. The 'pretension' that I mentioned about the notion of 'rules light' is that the designers of rules light frequently think that they are offering up artisanal haute cuisine rules that obsolete all other offerings, when in fact what they are actually selling is 'fast food' rules. There is nothing at all wrong with 'fast food', and there are times when well made fast food is exactly what the situation calls for. It's just by no means is 'fast food' proof you are a better designer than someone writing heavier systems, and by no means do 'rules light' systems obsolete crunchier ones.
