How so?
Few exclusive games, an underutilized back screen, and it's very pricy for a handheld. People (reasonably) expect handhelds to be priced lower than consoles, and the Vita wasn't.
It wasn't, on its own, a bad piece of hardware. But the price and fact that everyone already had a 3DS meant it failed to sell and thus failed to get any good games.
Also, damn Nintendo, didn't you just announce a bunch of games?