Appdating was already very popular in the gay scene, so i don't think it only works for straight women under 35..
Furthermore, I think that these apps mostly reflect reality.
In the offline world fat people would have a hard time finding dates too. Don't you think?
The gay scene is very different; casual sex is far more normalized so everyone is getting laid more often. Queer dating is its own thing (I'm trans so I've dated as pretty much every gender / orientation at some point in my life). My experience when I was seen as a gay man is that it's actually hard to use the apps for "dating" versus casual sex -- so many people are just looking for sex that you'll just get your heart broken over and over again until you, too lower your expectations and stop hoping for more out of the apps.
The apps simply reflect peoples' superficial preferences. It's way easier to swipe left on a photo of a fat guy than it is to reject a fat guy who you find attractive because he is kind and makes you laugh. Personality really is most of it, but personality doesn't come through in apps.
The problem is that eventually they at least offline find someone. But on apps you can just wait a bit longer, spend a bit more time/money and hope to get lucky.
Most of the problems with online social networks and dating apps are not brand new, just a lot more severe.
Furthermore, I think that these apps mostly reflect reality. In the offline world fat people would have a hard time finding dates too. Don't you think?