What RUINED Don Bluth Animation?

https://www.youtube.com/watch?v=xRBRNoc_Ybw

Don Bluth was the first, true rival Disney animation ever faced. He went head-to-head with them releasing movies on the same date as Disney's films. Despite putting up a fight, his success ran out and went down hill. Why did this happen? What exactly ruined Don Bluth's run against Disney?