Actually, yes. There was an attempt at an All Pro line of football titles with classic players but it didn't fare so well. And let's not ignore that Midway tried to reinvigorate Blitz with Blitz: The League prior to going under and I think Blitz is still alive and well under new ownership. Then there was Konami and its Disney Sports line. Tecmo Bowl Throwback specifically brought that series back from the dead. EA itself tried to do the NFL Street thing, too. If you want to look at different sports there were similar basketball games like Hoopz, recent NBA Jam outings, Mario Hoops 3 on 3, etc. Baseball has Mario Super Sluggers, I don't know if the Backyard Baseball games are still being made but they were not too long ago. The sports game landscape is faaaar more robust than EA's main line. To say that the RPG genre isn't mainstream because, for example, the PSP is a dumping ground for RPGs that push middling numbers is no different than saying sports games aren't mainstream because most people don't pay attention to anything outside of EA's flagships.
If you think I'm being unfair limiting it to football and you want to expand it to the entire sports genre you end up with EA's major franchises doing amazingly well with all kinds of fringe titles not getting nearly as much focus from the same crowd. It's no different from the RPG landscape in that regard, with a bunch of major titles pushing phenomenal numbers while the PSP (currently a bit of a niche system itself) and it's slew of budget RPGs push niche numbers. Of course games like Hexyz Force and Ys are going to be niche titles. 1) They're on the PSP. 2) They're budget games with little to no advertising. 3) They're decidedly last gen in presentation. All of those factors matter a hell of a lot more than them being RPGs. What, just because there's so many of them that ends up outweighing the mainstreamness (a word?) of the genre as a whole?