@Celebrim It seems you’re advocating for one universal system for RPGs and then supplemental settings/scenarios/adventures for that system as the main focus of additional products.
Not at all. There is no one perfect system. However, at this point in the development of rules technology there are known to be several very robust systems with their own strengths. To name a few, we have D20, BRP, PbtA, Gumshoe, WEG D6, HERO, Cortex Plus, FATE, etc. And each of those has several variants and there are a number of robust independent game systems that could support new setting treatments - Dogs in the Vineyard has a system that I think could easily be adopted to classic Star Trek, for example.
What I am saying is that at this point in time it's largely wasted effort to go out and reinvent the wheel. The vast majority of effort in professional publications is being spent on producing new rules. I think this is happening because producing new rules is relatively easy and its fun, and as a rulesmith myself I totally get the need to write down your clever ideas for a rules set. But it's still mostly wasted effort that largely duplicates what is already out there and divides the community amongst a bunch of rules sets, most of which almost no one will ever play. For whatever sort of story you want to tell, or you want to help others to tell, there is a ruleset out there that does the job well enough.
What most rules systems actually lack is truly robust and well thought out examples of play. I've been harping on this for like 20 years now, and it just keeps being driven home for me who much effort we put into rules and how little effort we put into scenarios for those rules.
For example, about 2 years ago I decided to run a Call of Cthulhu campaign and that I didn't want to homebrew the scenarios because I was burned out from writing. Call of Cthulhu is ironically a system that is known for having invested much more effort into creating its scenarios than its rules, which is IMO (along with the robust BRP rules set) is exactly why CoC has remained relevant for so long. But even when exploring what's available as scenarios in BRP, I was shocked by how few scenarios out there are really well done and how much work I had to put into even the most classic scenarios to make them really pop. Many scenarios which I'd heard about when inspected turned out to have serious flaws, and even fewer of them really captured anything like what I would associate with the core ideas of HP Lovecraft's 'Cosmic Horror'. What I ended up running had moments of fun, but ultimately I found it disappointing because the examples of play I was being provided really weren't up to the challenge of presenting the game I wanted to present. And it wasn't obvious to me how to go about presenting the game I wanted to present. Whatever the solution was, I realized it was hard, and doing something hard was exactly the opposite of what I wanted at the time, which was to pick up a text and with minimal effort turn that text into a game.
Leaving aside my problems with the subject matter of the scenarios, even Seth Skorkowsky - who seems to be one of the the world's leading expert on running the system - when reviewing these scenarios frequently makes note of the serious and yet obvious flaws that CoC scenarios often have and has extensive useful notes to the would be GM as to what they will need to prepare or alter from the scenario to get good results in play. And this is in a system that has spent more than the usual amount of money and effort on having examples of play available. It seems the vast majority of rulesets exist as rules only, with no real examples of play.
There is just a dearth of really good writing out there. There is not a dearth of good rule sets. Indeed, one lt;dr summary of what I'm saying is that pursuit of the perfect rules set is a false goal that really needs to die. I'm not necessarily saying that investigation of rules technology should come to a stop, as I think that there are plenty of well thought out subsystems that will always need to be created to support various minigames that become more central to play in a particular system than usual, but I am saying that I'm not really that interested in new rule systems.