Although it’s been about 30 years between the first season of the show and Mighty Morphin Power Rangers: Once & Always, it’s a bit strange that the CGI effects haven't evolved much. While Mighty Morphin Power Rangers will always hold a nostalgic place in the Power Rangers canon, it’s also true that the effects and dialogue tended to err on the campy side. This is a positive feature of the series, but the effects have naturally improved with time. For that reason, there was obviously an expectation for the reunion movie to differ considerably from the original show in this regard.

https://screenrant.com/power-rangers-once-always-cgi-looks-old/