It's nothing complex, it's that the ye olde game sniper class always fucking sucked. Literally every class based shooter has the sniper class and every edgy teenager immediately locked it in, ran off to the farthest corner of the map, and began plinking off headshots for 20 years straight and by now he's so good at it he could shoot god out from heaven.

It's fucked up because TF2 is unironically better than a lot of them, at least the maps are fairly tight and there was an attempt at making a hard counter class. In every other game you were just expected to play the luck of the draw as to whether sniper island was looking in your direction or not with nothing you could really do against them.
It was just always the worst element of these games but any time you asked "so what classes?" it was always "uhh basic soldier guy... heavy machine gun guy... like, a recon dude... oh yeah, and a sniper!" because of course they would, everyone put a sniper in. And it always sucked.