it’s been over 10 years, no other edition came close to having good sales for more than a year or two. When does the short term end?
Ten years IS the short term.
Have you not noticed the negative responses to 5.5e? Have you not seen how things are splintering, folks are re-evaluating their commitments, sales aren't being crowed about from the rooftops, etc., etc.?
For someone like me, who credits a lot of the success of 5th Edition to a combination of luck and timing, it's really quite clear the honeymoon is over and folks aren't satisfied anymore. 5.5e will last a while, because a (first) re-release always does that.
"It succeeded so it will always succeed forever and everything after this should imitate it as closely as possible" is a really bad policy. It screwed Disney with Star Wars. It screwed Marvel Studios (not coincidentally
also part of Disney) with the supersaturation of Iron Man clones that didn't have what the original had.
"5e was a success" isn't an argument that's going to get a lot of traction with me, more or less. Sure, what's past is prologue, but
things change. If you think those changes don't matter, you're gonna have to actually bring evidence to the table. I've personally seen this exact effect happen to multiple different kinds of games--single-player video games, multiplayer video games, tabletop games, even in the board game sphere.
Simplification above all was the mantra of the late 2000s and 2010s. It cut through a lot of crufty crap that had been around for a while in various media. Early on, it was mostly removing stuff that really wasn't pulling its own weight. Unfortunately, when you've removed all the crufty crap, you start cutting into the actual muscle of the game--and I've seen developers and designers do that a dozen times or more at this point. I am not one who uses the phrase "dumbing down", because I dislike it as treating all simplification as bad. But it really is the case that simplification can be taken too far.
I am very much of the opinion that the buying public has, over time, decided that 5e was simplification taken too far. Again in my own personal experience, the thing I hear from
tons of people, across a wide gulf of interest, personal history, and rules-preferences, is that D&D 5th Edition does not give them enough personal expression in how they
build their characters. Fluff has always been infinitely free to do whatever you wish, so long as your GM doesn't veto you. What you actually
build your character with is where your choices get actually put to the test, since 5e provides no mechanical structure for any other way to be put to the test. That's where you get choices that are clearly, concretely
expressing something--and giving actual
feedback on that choice, rather than tying a pretty ribbon to it and moving on.
I don’t think anyone said ‘all simple all the time’. Also, a game is not evergreen when the same 500k people keep playing it for two decades, it is evergreen when it keeps attracting new players for two decades
People are specifically talking about making every class more simple than it already is. That's the essence of "all simple all the time".