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.
It does not only inspire ire like you think. I’ve been at these rides, and I’ve seen people waving at us from their doors and windows, I’ve seen random people join in, and I’ve even seen some (cool) drivers stop and just vibe along with the parade.
Some drivers don’t like it, but the beauty of critical mass is how 1. Cyclists feel safer when there’s a critical mass of them, and 2. In this event, drivers see that they’re in the minority, which is a perspective change for any onlooker and for some of the more agreeable drivers as well.
At most of these rides, some cyclists can be rude (and it’s annoying af but understandable) but I think the majority are trying to just show what a good time we’re all having and respect the laws of traffic and other road users, to the extent that while we have the right of way to continue through red lights once the lead group has entered the intersection, we try to keep people riding on the right side of the road.