One of the possible reasons for this is that there were cheap pirated Genesis games available[2], which, i think, SNES games were much more expensive, probably not pirated.
[1]: The graphics and fluidity of Donkey Kong Country on that console were mesmerizing for a Genesis player though :D. But for some reason i always preferred the Genesis sounds and music. And, of course, Sonic The Hedgehog!
[2]: I actually didn't know about this till not too long ago. I always thought my Sega games were original! But learning about this explained why "save slots" didn't work on any game (the pirated cartridges didn't have a persistent writable memory).