I dont get the point of these movies existing if they aren't canon
Like wtf bruh
They are not canon in relation to the manga, but each movie is canon of itself.
Or, in other words, each movie can be seen as a fictional story by itself, just like any other original movie, so they have their own value as artistic works.
And if Oda is really involved in the production of the movie, the story can even somehow be seen as an alternative story.
So it's definitely not part of the main story in the manga, but it can still be somehow seen as part of One Piece as a series as a whole. Or at least that's how I perceive it.
The same can be said about Jojo;
What happens in Part 7 is not canon in relation to the previous parts; It's not like the story is even supposedly occurring in a parallel dimension of the one in the other parts; Part 7 is a new fictional story, happening in its own universe, with no relation to the one of the previous parts, but this doesn't stop it from still being part of the Jojo series, because it was written by the original author of the series, and was given the name of Jojo as well.