It's very possible they had issues with cramming all the data into memory on a poor console. Do you know how much ram a 360 has? Sure you can say "Oh but they don't have windows overhead and they're dedicated to games and it's not the processor and.." but at some point you have to stop and go "wait, 512 megs? You mean 5.12 gigs, right? No? Oh, damn."
The PS3 is apparently far worse, cutting access to the memory it has so games are in tiny tiny memory spaces. That's presumably why Skyrim kept barfing all over itself on that system.
Because lots of people play on the consoles, because they'd use a PS3 or xbox controller, rather than a keyboard and mouse for games like these. It makes more money for the devs, which is lately more important than quality.
I started with SR3 and then went back to play SR2 for the story. However, I do like SR3 better. For me, it just plays better.And it seems that making an unstable game with lots of adverts (and horrible DLCs) does work, as seen on SR3, yet SR2 and SR1 are completely abandoned, hardly anyone who played SR3 first wants to know what/how SR2/SR1 is.
I started with SR3 and then went back to play SR2 for the story. However, I do like SR3 better. For me, it just plays better.