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.
Running people over is also illegal. A defensive driver would stop and wait for the road obstruction to clear, or take a wide-berth, safe alternative path around it.
Why can’t the bikers stay in the right lanes. What about anyone walking, get out the way and fuck them too.