My guess is they're contract ran out on how many episodes they were going to make so it was either continue with different actors etc. or which i doubt they went off because of low rating which happens pretty often some series get taken off before they get started like The Tick
My guess would be that they brought the series as far as it would go, and/or they were losing viewers. They also could have been losing a few people in the cast to do the voices. I like how they wrapped it all up with the view of the future. That was really nice, except for the typical Jean Grey/phoenix thing. I mean, can't anyone leave that untouched!!
