Okay, here's some real talk from a professional game developer and publisher. As I have a tendency to, I'm gonna speak directly to the OP.
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.
You aren't wrong, and it's closer to two decades.
D&D 5E is already much simpler than previous editions like 3E and 2E, yet people still look for even lighter systems up to a point that for large parts of the you are freeforming with no mechanics at all.
You are mischaracterizing "rules-lite" and "story games". Most of them have BAD mechanics. Others, like Fiasco, aren't RPGs at all (Fiasco is an "exquisite corpse" or "spanking yoda" game with dice, it shares more DNA with Apples to Apples than Dungeons & Dragons). To be clear, I'm not biased against this genre. My own
Anathema is a storygame of Forge vintage. My own
Dicepunk System is something I often advertise as rules-lite (although it's more like rules-medium, it IS substantially simpler than D&D 5E).
Have people grown up, gotten jobs and dont have time/interest to learn rules anymore?
Well, yes. So you already knew at least part of the answer to your own question, I see.
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?
No. Here's the truth:
accessibility.
"The average tabletop roleplaying gamer has at least close to genius IQ."
If you were to create a graph tracking the truth of that statement, with a timeline from the 1970s until 2019, you would watch the truth plummet continuously. At the same time:
"Virtually no one plays roleplaying games."
If you were to graph the truth of that statement over the same timeline, it would do the same thing.
You see where I'm going with this? The gates are opening. You don't need to be a genius, or even smart, to play RPGs. This "dumbing down" outright frightens some people, even people who don't necessarily understand what it is they're frightened of, and it's very reasonable for them to be frightened. But it makes perfect sense from a marketing perspective. When you reduce the barrier to entry, younger and dumber people can play the game, you get more sales, and you grow the hobby.
5E Worked.
There is something I like to call "bounce rate", which is the percent chance someone will try their first RPG, decide it's not for them, and never play an RPG again. 5E has the lowest "bounce rate" of any edition of D&D ever. While other factors effect it, primarily GM skill (specifically spotlight management skill, also skill at creating a welcoming atmosphere), the most important thing to understand is that bounce rate is directly related to complexity. The people who make D&D want an edition of D&D that doesn't scare people away with too many rules.
BUT THAT IS NOT ALL
See, while I would hope we all want to grow the hobby, I personally don't have a financial stake in how many D&D books sell, and I prefer to play with very smart people. Right now, I am running D&D 5E because it's what everyone is playing but if I could get the same turnout for 3.5E I would do so in a heartbeat. In a sense I was just born a little too late, or maybe got into the hobby a little too late. It would have been awesome to be part of Living Greyhawk...but I digress.
So why do I care about rules not being too complex?
Speed of play.
As an example, here is a complexity problem that both D&D 3.5 had that D&D 5E has improved upon. In D&D 3.5 every single spell is a special snowflake which totally unique rules all of which are slightly different from every other. There is no consistency to them. And there are a TON of them. Many of them with their own tables. So even if you have the mental capacity to memorize the spells that are commonly used, how many spells can you really memorize that way? Not enough that you don't wind up flipping through the PHB multiple times per session. 5th Edition didn't fix this completely, but it did improve upon it. First off, the number of spells was reduced, while the ability to use higher level spell slots to amplify lower level effects (my favorite examples being
sleep and
magic missile, especially
sleep) was introduced. Big improvement right there. Secondly, they added at least a degree of consistency. In 3.5 a spell might or might not require a ranged touch attack roll and/or allow for a save and/or care about spell resistance and/or have some orthogonal means of resolution. In 5th Edition, generally, offensive spells either call for a spell attack roll OR allow for a save. Very few spells fall into the "both", "neither", or "other" category. Spell resistance has been stripped down to certain monsters having advantage on saving throws which is simpler and more elegant. When spells do violate these "rules", they're usually well known cases, like again,
sleep and
magic missile. The former effects 5d8 hit points of monsters in the area, starting with the enemy with the lowest hit points. There is no roll to attack, and no save.
Magic missile always hits, requiring no attack roll, and allowing for no save, but if there is anything virtually every D&D player from any edition knows about the rules of D&D, it's that that is how
magic missile works and has always worked.
You
can shed complexity without shedding granularity. I would argue that 5th has done very well at this.
So, speaking as someone who has done this (and pretty much nothing else) for a living/for a career since 2011...5E is objectively a better game than Pathfinder or 3.5E. But I personally would rather play 3.X than 5E because I know it and love it, even for all its many, many, many flaws.
Final consideration:
the simpler a game is, the easier it is to balance.