YouTube is getting really bad, so it's difficult to blame them for leaving. I guess many people are oblivious to YouTube's enshittification. However, as far as I know, most of Nebula's creators are still on YouTube, and they have way more videos, so I'm not sure how these guys think this is going to work out. It will almost certainly arrest any growth they had.
I think this YouTube comment really explains the backlash very well.
The problem with this isn't just that they're paywalling their stuff. It's the "why" that REALLY made this sting. They are guys that came from Buzzfeed. An online entity that was destroyed by over hiring, inefficient spending, and mismanagement. They have over 20 employees, in a MASSIVE office space, in one of the most expensive cities on earth, all to make shows that are literally two guys in a room goofing off the VAST majority of the time. They mismanaged their business, and instead of sucking it up, admitting they didn't learn their lesson from Buzzfeed and downsizing, they decided to paywall all their content after having a patreon, adsense, a merch store, live events, and literal 5 minute ad reads on every video. Rather than accept the obvious conclusion, which is that they need to completely rethink their business model; they keep asking the audience to enable them.