I think solely because it does have games. Wii U did not have a big library at all. It was also generally popular in Japan, hence all the game support it got, but over here, it didn't do particularly well...The Vita has something around 1400 games on it going by wikipedia. Wii U had 700 and the Vita is still getting games. The Vita is this weird system that didn't do well, but had such fan support, despite Sony eventually ignoring the handheld. The Vita is supposed to be the best for JRPG's and such from what I understand, which is probably why it did as well it did over here.
While it does have more games and a larger library, i feel the Wii U's library is way more diverse. Vita seems to be 70-80 percent JRPG. Which is awesome but some people like party games, action adventure, racing and such. And vita is very limited in those . I think Wii U has a more rounded and more iconic library of games. But in fairness i havent dove too deep into the Vita's library so i might just be biased. .
those numbers are way off I Might be the biggest vita collector in my country (not saying I am but I actualy might) and your numbers are way of at least with english releases I would say about 50% is jrpg and that is an high estimate mind you. and the vita actualy has quite a lot of racing games more then the wiiu at least
wrc 3 4 and 5 need for speed sonic all star racing ben 10 galactic racing and I know I forget a few.
the vita has some cool fighting games too and even games like civilisation and some awesome mosou games.
My goal is to have an copy of every physical released game thats playable in english and with the games that are on the way I should be around 80% of that goal.
also its not fair to compare libaries yet since the vita still gets games every month and the wiiu is just dead.
the vita libary has all kinds of games and yeah japanese rpg is the biggest genre but far from the only one
and yes the vita is a commercial failure mostly due to sony being relay stupid about it but the vita is an amazing system
and for the people who dont believe me I am big in on vita this should prove it:)
http://imgur.com/a/KC7eiand yes this was my collection 2 weeks agoo or so:P