I cannot relate to this as I never followed Jack Black much. I am curious as to what people's opinons are - don't downvote this if you think it's my opinion, lol, because it isn't, but I thought it was spicy and I could see some interesting Fediverse feedback.
I dunno, i can relate. I find his performances in things now to be very insufferable. He clearly just checks some marketability boxes and has flanderized himself to be safe enough to keep collecting those Claptrap and Minecraft-Steve paychecks.
It feels foolish because any idol will dissapoint you, and JB never seemed like a figure you should invest much emotion in. But you listen to old Tenacious D songs and part of "the act" is that JB and KG are friends on a level those goes beyond any other notion of fraternity and friendship. The songs are about the earth-shaking power of their bond.
So to see JB casually throw that away over a stupid joke, it reveals the artifice of the whole enterprise. And that sucks, its like when the couple you've known for 15 years, married since high school, get divorced and then you find out that actually he was abusive and the whole perfect loving relationship was a front. It tears up an example of a good relationship you didn't realize was your model and makes you question if you really understood to begin with.