At least in Argentina, the Megadrive was the console of choice back in the day, almost everyone and their dog had a Megadrive, but only a few had a SNES.
The reason was probably because of marketing and sports games.
In general Megadrive had way better sport games, and people probably liked that.
I think it actually fared quite better than the SNES, even when the latter had better hardware, graphics and specially sound.
The Megadrive had great platform and arcade games, but it was notably behind in the adventure and RPG department, I think it suited different tastes.