In another of D&D Beyond's frequent data shares, here is a look at the most popular fighter subclasses currently in use. The Champion leads the pack, followed by Battlemaster, Eldritch Knight, Gunslinger, and Samurai.
This is exactly what I was thinking.Seeing the top 3 be the ones that are in the PHB is hardly surprising. The Champion being most popular is possibly in part down to it being the only one in the Basic Rules.
Whew so the stereotype of those player who "just want to play a plain fighter" (I got one at my table) is actually true. What I find amazing is that so many want to play a gunslinger or a samurai.
But the EK, Gunslinger,Samurai, AA block may suggest there is a huge block of people who want to play nontradional fighters.
You say the EK and AA are "non-traditional", but I think they're actually extremely traditional, and just the result of 5E having a multiclassing system that isn't very compatible with a lot of traditional D&D ideas, like the Fighter/Mage. Since D&D was fairly young, loads of people have wanted to play "gishes" and so on - characters who combine arcane magic and fighting. Some pre-AD&D versions had all Elves be that way, as a class, 1E and 2E had multi-classing (which worked really surprisingly well, looking back I'm shocked at how few balance problems it caused), 3E's MC system meant that it ended up having to develop specific classes and PrCs to allow this (because just stacking levels of Fighter and Wizard was pretty rubbish, mechanically). 4E had multiple specific classes which allowed it, including the totally wonderful Swordmage, perhaps the best incarnation of the "Fighter/Mage" in many ways. 5E saw the problem coming, and presumably after deciding to use a 3E-style MC system (booo! pretty sure there was a better one in one of the playtests), put in EK and AA to cover that issue.
The most interesting thing I see, personally, is that the Rune Knight, a UA class which is still playtest content, is about as popular as the Cavalier (a subclass that's been out much longer and is official) and way more popular than the Purple Dragon Knight, which has been out far, far longer and is official.