It's all about being human.
Some beautiful girls are elitist towards ugly girls. They feel they are better than them, and they show it, one way or another. Some ugly girls envy the beautiful girls. They feel they are inferior to them, and they show it, one way or another.
Older people might dislike new things because they were living in different circumstances when they were young. It might be envy, it might be elitism, it varies.
Younger people might dislike old things because they are living in different circumstances. They are not used to something so old - the current is more convenient.
In the Internet people tend to make themselves heard more. They have a 'mask' to hide behind to. Nothing will happen to them as long as they are behind that 'mask.'
They can call names, they can be dicks and leave mid-game, it's their own digital world - they can do anything they want.
Some people think like that.
However, DON'T GENERALIZE.
The people who make themselves heard about their opinions are only a minority. The people who don't care about other girls' make-up masks and the people who don't care about when someone was born don't tend to make themselves heard. There's only that one guy "hating"... What about all the others? They're just silently playing, ignoring the person. In fact, it feels twice as satisfying to defeat a person who's just being a nuisance and watch him ragequit. Hell fucking yes. Even if it's "just a digital world."
There are always those dicks who want to ruin others' fun. Why do they do it? It's impossible to say since they might have their own circumstances. Some might be in the rebellious phase of youth, some might have actual troubles in real life and they want to run away from them. Some want attention, some simply want to have a fair match but have a wrong image of it. They all have their own reasons be it simple or something deeper. I wouldn't dwell into them too much.