Why doesn't holden have a good time at ernies?

Holden Caulfield doesn't have a good time at Ernie's because he feels alienated and disconnected from the people around him. He is critical of the phoniness he perceives in the other patrons, which amplifies his sense of isolation. Instead of enjoying the music and atmosphere, he is consumed by his disdain for the crowd and his own feelings of loneliness. This combination of factors prevents him from experiencing any genuine enjoyment during the night out.