Yea, so you get another hour of game play. Whoopie doo.
If you play through a game, watch the credits, say to yourself 'well that's that', possibly even uninstall, then read that the ending you played wasn't the best ending, what do you do? You either ignore it (with irritation) or you 'rewind' the game - which is akin to a sort of 'hack' and it damages the overall experience.
I'm not against multiple endings per-se, but I think they're problematic for the player.