It's because gaming is available to anyone, these people think it's not worth it. Too bad the ones talking are usually the ones not doing anything worthwhile.
Gaming as a whole is a weird thing, there's this group of people who are just stupid that think "Lol it's just a video game" where in fact it's just a sorry excuse for them not doing anything with the game they play and it makes them feel better. It's not exclusive to the FGC. Just because you have the option to play the same games as someone better than you doesn't make you an equal.
Sports/athletes are viewed different because not any scrub can just go and play in the NBA, NFL etc, but any scrub can buy a game, and play so they think it's equal or the same as what they're doing as people who are playing at a different level, when it's not.
No one likes to feel devalued or "someone is better than them feeling" so everyone lumps gaming accomplishments as nothing spectacular because everyone has access. When in fact, yes, some of us just are average and other players are just better. Myself included.