I used to watch it in the 50's and 60's, until I found out it was as phony as wrestling. Even as a child, I noticed how the home team would always win on the last jam, or whatever they called it. Wrestling is still phony of course, but I have heard that roller derby changed.
Not that I ever cared or watched but I talked to a number of spectators of both disciplines and they all knew them as the typical good team vs. bad team waste of TV time. As far as them continuing to watch is a mystery.
If anything I watch UFC and MMA fights which are real unless some TV tough guy would even be allowed to step into the cage and try to last 1 minute without his head getting torn off.