i have a gf2 as well, mx400 64mb to be exact, and i hate it, but im thinking the answer to your question is that the sports games are not as big so they compensate by trying to make good quality graphics (also everyone wants high realism when playing sport games such as racing car games), but with other games such as the bf series they have to concerntrate more on other things such as balance, anti cheat, all that sorta stuff.
its weird, i can play hl2 with high texture and other stuff, but i get lag on bfv on low EVERY THING eg 640*480 (i think thats the one, i dont no the ratios all to well)