Everything relies on the sales of toys. Power Rangers is a show that is basically one big commercial. All that the executives care about are the sales of the toys. KRDK is in the same boat. If the toys don't sell then there will be no sequel or anything continuing after it. That is why RPM is the final Ranger season. The toys have not been selling as much as they used to.
This is something I think all of you should read. This is an interview with the creator Steve Wang. He talks about the show and what he plans to do in the future.
http://www.scifijapan.com/articles/2...us-television/