Well there are different "continuities" for each Marvel and DC hero, aren't there? (Meaning, different series of comics and TV shows that, while dealing with the same characters, change certain things about the setting. For example with TV, the different Batman, Ironman and Spiderman shows. Or with comics, Marvel's Civil War.) I always thought the yearly entries of the franchise tokus could be equated to that.
I'm pretty sure Civil War is continuity (unless it's been retconned? It was never alt-universe, though) There have been alt-universe comics like Ultimates and All-Star and the Marvel "Mangaverse" (shudder), but to my knowledge, attempts at making ongoing alt-continuities tend not to be sustainable. The reason cited for this is basically that American fans don't want to read about an "alternate" Spidey. They want to read about the "real" Spidey, or it's a waste of their time. (Despite all the problems it would solve if multiple Spideys were just allowed to exist in separate universes!)
As for taking the TV/movie adaptations as equivalent to "this year's model" of KR or Sentai is that in western comics, well, it's an extension of the same problem. Because there's
always going to be a "true" version of the character running in the comics, and the fans are incredibly loyal to that version, adaptations simply aren't going to be allowed to stray that far from the character's baseline. Spider-Man will always be Peter Parker, who will always be a geek living in New York, working for J. Jonah Jameson, and hanging out with his Aunt May. He'll wall-climb and web-sling, battle the Green Goblin and Dr. Octopus, and crush on either Mary Jane or Gwen Stacy.
And so there's never going to be a crossover where the Spider-Man of Amazing Spidey meets Ultimates Spidey meets Raimi Spidey meets Spectacular Spidey. The characters and their worlds can be changed and fine-tuned and modernized, but they're just never going to be that distinct.
(At least with A-list heroes. B-list heroes are a different story, but that's a whole other rant.)
Anyway, the point is, there are people who get really really invested in the "real" version being something reliable and permanent and untouchable. They love the shared world/sliding timeline/40+ year continuity aspect of western superheroes. For people like that, I imagine Tokusatsu's yearly reboots could just make it seem hollow and pointless. After all, what's the point of getting invested in this grand epic story if it's just going to...
end?