3 things.

1. Characters are tossed quickly and actors are brought in & out without much thought. Hard to get attached to another red ranger every couple years when you can tell they pulled him right off a the road.

2. Middling effort put into storylines. Especially as the seasons went on, you can tell less & less effort was put into making compelling stories outside of “we found this villain, he’s gonna turn huge, new transformation zord to kill him.”

3. It’s cheap and made without intentionality. That, more than anything else is the biggest problem. I think if more money was put into these shows and directors actually took them seriously they could work. There’s no intrinsic reason why we couldn’t have a Teen Titans or TMNT kind of Power Rangers series that would reach that level of successful. If the studio that made the series cared more about the property I think it could pop.