Well, the show may have even ended after Season 1 if there wasn't such a fandom for it. Just look at the length of the previous generations. As said above, it is all about money. Just another note, although this probably isn't going to happen, should G4 end and G5 come into play, it should feature Apple Bloom and the rest of the crusaders as the new 'Mane 6' (since Babs Seed became friends with two other blank flanks, likely to be a unicorn and a pegasus).