I'm assuming your speaking of charity events held in a theatre, yes?
For many of these events, there's usually a lot of work that has to be done in order for the event to be pulled off. Sometimes additional equipment has to be brought into the theatre, set-up, operated, and struck. It can take hours of work to do this. In most cases, the crew doesn't have the option of saying no. If they're part of the house crew, then they're under obligation to be there. No matter if they want to participate or not.
A performer can come in, sometimes without rehearsal, sing their song and leave.
I've rarely worked a charity event where the musicians haven't been paid for their time.
Most of the time, it's just the performers who offer their services gratis, and sometimes it takes a lot of phone calls to find performers who are willing to do so.
Do you take exception that caterers, florist, waiters, bartenders, etc. Get paid when doing charity events. Or is it only the stagehands that you have an issue with?
"Just a Guy. Your feelings are touching. I am gladdened by the thought that you will one day wind up 6 feet under as we all do." - MrRoxy ------
"I do not suggest you walk out the door onto a New York street with your vulnerable child part exposed and not protected..." - Jason Bennett