They're canon only in a Trek universe, not the Trek universe.

No wait... if history is the same as reality to a point, wouldn't they still be canon? Like someone could be like "Hey, computer, play me something popular from mid 20th century earth." And it just happens to find Brass Monkey?

I know I'll catch flak for this but they're what got me into Star Trek. I was completely unfamiliar with it and the movies were fun so I got into the shows. Obviously they share very little besides a vague aesthetic but the movies were a good bridge for me as a teenager

Maybe the movies weren’t the greatest but I actually really enjoy the kelvin timeline. We have so many alternate takes on reality in Trek (mirror universe terran empire timeline, mirror universe coalition timeline, Picard alternate reality confederacy timeline, kelvin timeline) and this is one of the more interesting ones in my opinion.

The others basically explore dystopias, while the kelvin line is still a hopeful and optimistic one, despite the differences in federation doctrine and technological developments.