Though the EU PSN Store has over 100 PSOne titles, the US store has around 9, Sony explains why, more details inside.........
The US PSN store has only 9 directly downloadable PS Vita compatible PSOne titles while the EU store has over a 100, Sony have revealed why this is:
Each territory is completely unique and must go through its own individual processes for approvals in order to be available for purchase directly on PS Vita through PlayStation Store. We work collaboratively with all parties involved, including third party publishers, to ensure that we are following the proper protocol. As of right now, there are nine PS one classics titles available on the PS Vita store, however we are working hard to expand this list as soon as possible.Let us know if this is an excuse or if its true in the comments below!
Source:
http://www.gamesradar.com/sony-explains-why-so-few-psone-classics-are-available-vita-us-store/