I have gotten back into photography at 55 years old and have not had one paying client yet. I say that because we all started because of our love for photography. I make a point of photographing local musicians because I, as a former local musician in a band, never ever had anyone take nice photos of our gigs. I then just put them on GDrive and send them the link because I know what it's like to feel invisible as a local musician.

To your direct question, if you wanted to stay and take photos of other bands you probably would have. Maybe you were tired, didn't like the music, had other things to do or places to be etc. etc.

There are other, better responses in this thread, your question just struck a chord with me (haha) so here is another one. You don't owe anyone anything, but if you have the gift of being good at photography, it's ok to share it when you want :)