In the first place, we still use and accept derogatory and blanketly dismissive words like "nerd", instead of more positive terminology that accepts and respects the worth of the medium like "movie buff", "sports fan", etc. Trying to reclaim the concept of "nerd culture" really just puts us further into that mocked and stereotyped box imo. It's the reason why The Big Bang Theory is a thing.
In gaming in particular you have the stereotype that these are "children's toys" and not "a viable artform", which we've spent thirty some-odd years trying and still not entirely succeeding to surmount. This is complicated by games that are just trying to be silly fun and not a provoking thought piece, like your DOOMs and WarioWares; there's nothing at all wrong with them, and quite frankly they're absolutely terrific, but people looking for their confirmation bias will gladly point at these examples and go, "See, it's all just a toy for children and manchildren, there's nothing serious here. You're an adult, why are you wasting your time on this stuff?" Then, you have people who genuinely mess up and drag the whole medium down with them. For every Braid or Hellblade you've got your David Lynches for people to laugh at and hold up as a token of why games aren't actually serious and will never be able to do what movies or some other "respectable" medium can. Thus gaming is not respected, and therefore ditto to its enthusiasts.
Oh, and add to this all your toxicity and hate issues, which have gotten a lot better over the years but in many ways are still pretty bad. Many people's mental image of "gaming" is still mic harassment on Xbox Live, and in many ways that still hasn't changed (just look at PC Overwatch). Also you have Gamergate, and some of the most popular personalities in the industry literally turning out to be hateful transphobes and white supremacists. This continues to steer wonderful and progressive people away from our hobby, sadly.
So, it's a combination of things really. Absolutely no excuse for homophobic slurs just because you like Star Wars though. Like, what the hell. That is messed up.