The documentary does mention it in a sideline, but the harsh truth is that in the 90's/early 00's, before the abundance of public skateparks, it always was skateboarders building the parks or ramps or fighting the red tape with the city to get a place to skate.
When it was all done, the rollerbladers kinda just showed up or at least that was what it felt like. And with that came certain entitlement for skateboarders and it really showed in not the best ways, especially with the homophobic insults, which 90's/00's was filled with and I hope we never go back to that.
Bladers waxing the coping was kinda the crutch of it all as co-existing in the same space wasn't always the easiest. It was also same with the BMXers with their steel pegs destroying the curbs/ramps.
And of course how these different toys operate don't always fit the same park and this led to some bummer sessions and didn't really make things better between different crews. In the 10's, after rollerblading kinda disappeared, the same thing happened with the scooter kids.
These days skateboarders are much more mellow policing the different spaces (despite it still being the skateboarders pushing things forward). As you get older, you can appreciate people getting rad no matter what they are riding. It still does suck when the coping is waxed, but at least you can approach it with a sense of nostalgia for the past, hah.