Could be a possibility, but you also had team-ups with 100% original footage for the Space/Lost Galaxy team-up and I think a lot of the others (bar Lost Galaxy/Lightspeed) were the same. But I'm guessing that Nickelodeon just doesn't have the same budget that Saban did in it's original era.
Did Saban part-own Fox Kids back in the day and that's why more original footage was created?
I assume Power Rangers was more profitable back then. Any show, the longer it runs, the more expensive it becomes. The franchise has done their best to reduce costs (actors being non-union, moving to New Zealand, reduced episode count, etc.) but because the popularity isn't the same, they don't have funds to make it like they used to be.
If the new Power Rangers movie becomes a huge hit, then I imagine we'll see better production values for the show.
Fingers crossed that the movie is a box office success so that the franchise gets a funds boost.So that Saban can use some of that money for the 25th anniversary episode.