Because they are trying to feed us shitty indie games which we can get for 10p on PC - no-one bought a vita for that purpose.
The last big western game they released I believe was KZ mercenary like a year ago.
Apart from that, its a lot of ports (not great ones either), and japanese stuff which if we are lucky then it comes to the west.
AAA third party games have dried up too compared to the first year.