I don't know, to the East of the Iron Curtain science fiction wasn't mostly about future optimism (at least after the initial "we're building a better society" optimism had been brutally murdered during the 1950s and 60s), but often a critical mirror of then-current society transported into the future to escape state censorship.

Maybe it's as simple as free societies not having the evolutionary pressure to produce great literature that requires an interested and intelligent reader to decode the hidden messages written between the lines ;)