This american version of the live action show was really popular in the era of the 1990's when it aired on Fox Kids. As Power Rangers continued, people got rather bored of it as the series had no end in sight making it go on forever just like Family Guy or The Simpsons. It looks like the show gave alot of people fatigue to the point were they do not want to keep up with it anymore and just move on to better live action TV shows or cartoons that have limited runs.
Forgot to reply to this earlier, but I only had like one or two issues with the 2017 film, but otherwise it was decent. Think the reason it failed though was because of the fatigue with gritty reboots there already was by then. That, and perhaps more childhood fans who initially outgrew the series moved on and never looked back, while people like me who returned to it out of nostalgia were a minority.
I dont know, but hope the next reboot film by Hasbro goes over better. The Battle for the Grid fighting game had grew increasingly popular. Power Rangers itself can still be popular too if they handle and market it well enough, like TMNT or any other superhero thing that isnt Marvel or DC.