[Matrixbeast]

The problem with continuity is the villain's escalation of force.
Many powers were never destroyed (The original dino coins (The Dino coins were replaced with the Ninja coins and those were the ones that were destroyed), the Zeo Crystals, the Red and Blue Turbo powers, the Astro morphers, the Galaxy Sabers, etc etc), so in the past, keeping a single continuity was accomplished because powers were passed on as the users changed.

But now, a single continuity fails because it will all circle back to "Why doesn't Tommy come and help?" "Why doesn't Wes come and help?" "Why doesn't Andros come and help?"
It'd be difficult to justify why past rangers who still have their powers intact would suddenly choose to be inactive, even when there's a new team of inexperienced rangers who could use the help and a new threat to humanity.

While having one single continuity would be nice, it would be incredibly high maintenance to keep straight.