Fighters are definitely a bit weird in the sense that they are both very generic and very narrow in their scope of abilities
True.
Prettymuch any hero from genre that doesn't cast spells/figure from history who wasn't a pacifist or literal thief, is most likely modeled in D&D as a fighter.
Yet, the Fighter has very few abilities - in even the editions most generous to it - beyond the very physical implied by great strength, not even the sorts of skills or extraordinary talents implied by military excellence (the Warlord got those in 4e) or political position (like a fuedal "Lord" the level title of a 9th level 1e fighter).
The consistent popularity of the fighter logically comes from the breadth, familiarity, & relateability of the archetypes it, more or less alone, is left to cover.
Not from it's mechanics which, though always lacking, have varied radically from one edition to another, without impacting that popularity.
Therefore, I think we should blame D&D itself for the fighter.
But what is "D&D Itself," when the current edition was designed using an open playtest, self-selected surveys, and social media to get input from it's existing fanbase?
that D&D has ultimately always been about combat foremost.
This has always been a criticism of D&D - and, by extension all RPGs, from TT to MMOs - and, while it's understandable, it's not really fair.
If we just look at page count, in the 5e PH Table of Contents, 'Combat' is 10 pages, 'Adventuring,' and 'Using Ability Scores' (including all skills), 8 pages each.
Now, admittedly, that's just headings. We could point to the Fighter, for instance, that all 16 of the Battlemaster's manuevers take up a whole page, indeed, of the 4 pages devoted to the fighter all but the couple column-inches taken by Remarkable Athlete, Student of War, & Know your Enemy combined, and the about half page each devoted to fluff and to the EK's spellcasting, are purely combat, so we could pad combat out to 13, on that class, alone.
Even so, the other two headings, combined, edge out combat by 3 pages.
Of course, it'd be quite the undertaking, but we could go through the remaining 72 pages of class descriptions, and evaluate how many of them are just about combat, as well. And then do the same for the 91 pages devoted to spells.