But the live-action movies did enormously well at the box office and the movie toylines were enormously profitable. Why change something that's doing great? Hell, Transformers and Transformers 2 were either the or among the biggest-scoring movies at the box office in their years!
I'd say they did well in spite of the awful scripts and designs. It's the uniqueness of the property that saved it. No other movie features giant shape-changing robots. If they'd come up with better looking robots and hired a good writer/director, the films would have been even more successful.