I didn't say everyone wants to play nonmagical fighters.
I say many want to play nonmagical fighters.
I don't think that is true, except for as you alluded to a few grodnards left over from earlier editions. I think most 5E players do not want non-magic characters of any kind.
I also said many don't like WOTC's OS design for nonmagical fighters.
I think this is true as far as the Champion and Battlemaster, but I think the lack of magic in them is itself the biggest problem with them.
WOTC straight up stopped making nonmagical fighters after XTGE. So it's Champion or Battlemaster as most people's only options for a nonmagical nonSamurai fighter unless your DM is running firearms.
In many if not most 5E campaings gunpowder or smokepowder itself is explicitly magical, so calling a gunslinger or firearms non-magical is a bit of a stretch in 5E. It is non-magical in some, but not most.
In Dragon Heist for example Dispel Magic will render firearms inoperable.
I agree that WOTC stopped making non-magic fighters and I think that is because most players don't want non-magic fighter. They will play them and make due by getting magic elsewhere, but I don't think players generally want that in the modern game.
That begs the question.
Are DMs allowing 3PP nonmagical fighter subclasses?
Few are IME.
I did play a non-magic 3P sublcass in one campaign. It was Zhentilar's finest and it was a blast, but it was not particularly powerful in combat, not any better than Battlemaster I don't think. It did have some cool things it brought to the table in terms of ability to intimidate people that was fun though. I also played as a Shaddar-Kai and multiclassed to a Fey Wanderer. So while it was a 3P "non-magic fighter subclass", it was not a non-magic PC.
That is the only 3P fighter subclass I have seen played personally.
If not, then a boom of fighters with nonmagical subclasses but magical feats and races to boost their versatility or power to want 5e fans want would be expected.
My suspicion is that many fans have adjusted those Old Fashioned Fighters with magic feats and races to update them. They'd prefer not to, hence the low Champion satisfaction score in 2020.
My suspicion is fans don't want non-magic PCs of any type. Boosting your fighter with race and feat options is not very powerful compared to other methods and in terms of feats, once you have chosen fighter and a non-magic subclass it is generally less flexible than non-magical feats like Skill Expert or Prodigy.
I think it is like someone said earlier, a fighter is iconic and people want to play a "fighter", but they don't want to play something that is tied to weapons and armor and skill checks and can't cast spells or use magic-flavored effects.
Obviously there are some leftovers from 1E or 3E that want that kind of PC, but I believe most don't in the modern game.