They voted with him. They, or enough of them on this occasion, have come round to the way of thinking that he has always had. He is the only person to have voted against every EU Treaty since the first one. Exactly the position in which some of them now revel was "Loony Left" back in the day.
Skinner can do as he likes, of course. No one who knows anything about anything can hold anything against him. That is not because he has been there so long. When I was first conscious of him, then he had been an MP for a bog standard 20 years or so. But he had already been a living legend throughout that period, and possibly longer. Some people are just born that way.