This was a Critical Mass event, which is why the bicyclists are taking up all of the street as a way to reclaim the streets and protest the lack of safety for riders under usual conditions. It’s not legal, but protests are never useful if they’re fully legal now, are they.
Go ride a bike.
I need to repair my bike. I do enjoy a bike ride every once in a while. But I do stop at 4 way stop intersections and yield to cars, because I know I’d lose in a game of chicken.