Eh, simple tribalism seems like a simpler answer to me. It's the reason Navy folks talk smack about Marines, Target shoppers look down on Walmart, Yankees fans bash the Red Sox, etc. — I don't see why it can't explain a React fan hating on Ember or whatever.
I think this is the right answer, it's pretty high level, and maybe more nuanced than "it's my tribe" because there's always infighting amongst the tribe, but it cuts to the chase, this whole attitude is endimic to the human condition.
Sometimes maturity cuts through it, but IME, sometimes it takes maturity and intelligence (though not a huge amount of it), and on the rare cases, there's something more, like a primal competitive nature.
