But the flaw in your reasoning, as I have already said, is that this only works as an explanation if absolutely every single thing, without exception, is what the greatest number of people sincerely, deeply want.
Do you know that? Do you know for sure that the greatest number of people is genuinely happy with every single thing in 5e, without exception, without even the slightest complaint or deviation on any point or part?
Because if you don't, then your position remains vulnerable to that simple critique: Just because someone buys something, doesn't mean they like EVERYTHING about it.
And we now have good reason to say that people actively choose to play things that AREN'T well-liked. We literally got statistics from WotC itself showing that there were problems with the satisfaction ratings for various classes and subclasses, despite some of those things being among the most popular options in 5e. How could that be? Is it, perhaps, that people choose things despite their design, even if that design continues to bug them and they just tolerate it because they don't have any other choices? Is it, perhaps, that with 5e being so thoroughly the (literal) only game in town for many people, folks settle for what they can get?
Except the overall culture of play for 5e is by far the most 3PP-hostile culture-of-play I've ever participated in. Even 3.x, which was notorious for its TERRIBAD 3PP (and even some terribad 1PP!), was more amenable to 3PP and outside homebrew options than 5e has been.
People celebrated how 5e was allegedly made for integrating 3PP in a way 4e wasn't. I've used more 4e 3PP and homebrew than I ever have in 5e. And at this point, I've actually played MORE 5e than 4e!