Curiously, movie does not actually explain why the powers had to be replaced, and it only establishes that the Rangers now had cool giant cars as their Zords.

Source: https://screenrant.com/mighty-morphin-power-rangers-complete-story-timeline/

Fern’s Orange Ranger origins were surprising, and it included a beloved had lost their Dino Zords at the end of season 2 when Red Ranger Zayto had to convert each Zord into pure energy.

Source: https://screenrant.com/power-rangers-cosmic-fury-orange-ranger-fern-first/

Turbo: A Power Rangers Movie, the first and so far only TV-canon theatrical film, saw the Rangers getting new Zords and costumes.

Source: https://screenrant.com/mighty-morphin-power-rangers-complete-story-timeline/