That is all true, I was just giving an example of cases where it's not necessarily worth it. Vita is far from that and there are indeed many exclusives that haven't been ported and probably will never be ported. There are also many games on Vita which aren't identically or mostly identically ported to a different platform. It's also a more unique platform than Xbox which is basically just a locked down PC.
If there's a port of one that's identical or otherwise runs identically it's less worth it for those. A platform like the Xbox one would basically be useless to emulate since every game is available elsewhere or if it isn't, not preservable (cloud games).