I can understand why those bands do it. It can be a hell of a lot of bloody fun. People are allowed to have a bit of fun after the age of 40, and a lot of them do need the money.
When actors get pigeonholed, that's their own doing to a large degree. Because if you do something that people like, obviously they're going to ask you to do it again. It's up to you to say no. If you're that insecure about working, you'll probably do what you're known to do.
A basic rule of life for reporters is that you should spend your time talking with and learning about people who are not sending you press releases, rather than those who are.

