It's really simple.  If I already have a system capable of playing Rayman Legends, why am I going to buy a Vita so I can play Rayman Legends?  Or Final Fantasy X HD, or Sly Cooper Thieves in Time, or PSASBR, and so on so forth.

The XBox 360 situation is way different.  Both consoles launched within a year of eachother.  So, when people were making the choice of what to buy, they likely didn't have either.  So, if I wanted to play Modern Warfare 4 I had to buy either a PS3 or an XBox 360.  From there, I'd look at exclusives or features I wanted.

The Vita on the other hand is came out something like 7 years after the 360 and 6 years after the PS3.  Most people in the Vita's target audience will have one of those two consoles.  If I have a PS3, why should I shell out 200-250 bucks to play games that I could already play?  If the portability is really that big of a factor to you, then buy a Vita, but for me, and many others judging by sales figures, that isn't the case.

What about who don't have a ps3?

If people want exclusive new ip why they don't buy Gravity Rush and  Soul Sacrifice.

The problem is most people who would be interested in the Vita do have a PS3, or at least a 360 which has a lot of the games. And if they don't have a PS3 they could buy one just about the same price (250 as opposed to 250 plus a memory card) if portability is not a big deal to them.  If portablility is a big deal to them, then you have the 3DS with a better library.  There are some people who are  better off with a Vita than a PS3, XBox 360, or 3DS, but that's a rather small amount of people.

Edit:  I wasn't talking about new IPs, but exclusives in general.  Of the top 20 games on the Vita, 14 are exclusives.  So, that says a lot about what people want.

The target demographic of dedicated handheld systems are, for the most part, "hardcore" gamers which probably already own 1 of the 3 main consoles. The people who are interested in a Vita already have a PS3 or a 360.

The few exclusives games that are available for the Vita are not exactly system sellers, one could argue that the only system sellers who can appeal to a bigger audience are Uncharted and Assassins Creed, and those games are indeed the highest selling games on the system. Games like Gravity Rush and Soul Sacrifice only appeal to a small audience, and going by the sales, we can assume this audience is indeed very small, thus the reason why the general consumer is not interested in those games. And imo a big marketing push won't make those exclusive niche games sell more.   

I want some proof to believe this.

Uhhhhh... you want some proof to belief what?  That people interested in the Vita are GAMERS and that they probably have purchased a GAME onsole in the last 7 years?  That the 3DS has a better library?  That the PS3 has a better library?  That the PS3 is $250 and around the same price as the Vita?  If you need evidence for any of these things, just look to common sense and you'll have your answer.  Or better yet, look at the Vita's sales figures, and you'll see clearly that its library is not appealing.

Wholy crap you didn't catch on my sarcasm xD

This by the way is what the Vita's library looks like after taking out multiplatform titles and titles not available in the US.  I know some titles are missing (Smart As for instance) but that just wasn't on the original list for some reason.  I may have accidentally Xed out one or two titles that should have been on here.  I wasn't sure on some Japanese titles, and I took 0 in US sales to mean it wasn't released here.  This isn't meant as a comprehensive thing, but just to give people a general idea of what the exclusive Vita lineup looks like.

Seems some people think that a handheld game without the name mario in it is not a game.

ps
sly should have 0.06 instead of 0.05 overall sale

Sony will never make a big new IP on handheld because people don't want them ,late port will not help vita but i'm sure multiplatform can help Vita.