Because sports fans are psychos is the very short answer. The former president didn't feel the need to suppress Ultra organisations, as he saw them as weekend warriors fighting one another.

It's quite common world wide that football ultras are among the best organised groups in their local arena. Same shit happened in Brazil, for the protests that ended up getting Jair elected - Despite the majority of demonstrators on the street being fairly left wing. The Ultras were organised cells, that managed to capture the movement and give Jair the much needed push to be a true contender