I live in a town with a busy music scene, and putting a band on is NOT a guarantee of a full house. There are lots of other much cheaper ways of entertaining an audience, like drinks promotions, televised sport and karaoke. There are more bands who want to play than there are slots to give them. I expect this is the case in most towns. Pubs usually have a monthly band budget, so people willing to play for nowt will get gigs, because the landlord can then maybe book more expensive band the following week. There is no minimum wage in the music industry so market forces prevail.

Festivals are completely different. My partner is a professional musician who plays in about 8 different bands to keep his head above, but he will do solo festival gigs for nothing as they expose his music to new audiences/bookers and can lead to solo bookings at clubs which pay better than his band work. This is a business and it's not one you are in, Lizzie. It's also obviously not one you understand.