2 reasons:

Main one: Japanese support is incredibly bad so far - really, for the PSP successor this is astonishing. Sales tell that story better than I could.

Secondary one: time. I'm buying more games now, than probably ever in my life. And time is not unlimited anymore!

Mostly three problems for me. One being the big games I am interested in, I can play in superior form on my PS3. Second problem being price. Factor in the required memory cards and the price is way too high. Lastly, I am content with my 3DS.

Too expensive. Although right now there's only like two or three games interesting me I'm not bothered by it because they'll come. They'll come, right?

My PSP died, I was going to get a PSV because i had accumulated a LOT of tip money, but I saw the 3DS was cheaper... and there were some 3DS games my girlfriend wanted to play, and I had a list of 3DS games I wanted to buy.

Not sure i'll get a Vita now.  Probably won't need more then one portable.

well there arent enough games for me, also the hole thing of bringing there main IP's to it isnt attracting me at all. yeah the idea of uncharted on the go is awesome, but not when its not developed by naughty dog and isnt as good as any of the 3 games on the ps3. i need more games like tear away, but the thing is i dont know if sony will keep making them in the future. i need atleast 5 ot 6 games that are considered more of a 90+ out of a 100 score plus with but loads of games with a 80+ score to make me get a vita. there are only three games that i really wanna play on the vita. tear away, escape plan and killzone (only if it has 24 or more players and warzone online multi[player). there are alot of games on the vita i would buy but they dont make me wanna buy the vita

The reasons I have not purchased a Vita, and most likely never will...

1.) The games are too similar to the experience I can already get on the current consoles.

2.) I have no interest whatsoever in touch-based control schemes.

3.) Overpriced and proprietary SD storage.

4.) No backwards compatibility with physical PSP games.