Could be a whole host of reasons. No one _likes_ to loose, of course, but some people really take it to the next level.
I've mentioned this in other threads, but I've personally noticed internet anger in general has really increased in the last half decade. Can't say exactly why, but a few associates of mine had an interesting theory that it's due to the rise in eSports.
Everyone wants to be the next big eSports star, and can't accept when they're really no where near that level. While I doubt that's the whole reason and everyone's reasons, I can certainly see it playing a role.