Wouldn't that kinda defeat the purpose of
A) selling ps2 classics to people who already own them but have no other choice (free money!)
B) Their entire PSNow service?
This would be amazing and I'm sure they could implement this if they wanted, but I'd assume they think this wouldn't be in their best interests so they decide to fuck the consumer. MS doesn't have a paid service for old games, hence why they have no problems giving us BC. I dunno if they would do it if they had the same service as Sony does. As for ps3 emulation, that would be incredibly difficult to attain with the differences in arquitecture but I guess that's a whole different subject.
It would be amazing for us, but at the end of the day they care more about selling remastered versions of their games then just let us play what we already payed for. As I no longer own a ps2 ou ps3 (both died on me even though they lasted many years)
I currently have no way to play old gtas, Devil May Cry 3, FFX, FF XII, SoTC, MGS2 and 3, Dark Souls 1..And guess what, some of these are getting remasters just so we have to buy it again, gtas being sold as if they were new, etc. It sucks, no apologies for this behaviour, but it's their call and they seem to be pretty confortable up there in the top, so they don't give a damn, ;/