The hint for fan says "Pan".
Here on the site version, it says both fan and pan.
Both are correct according to Naver.
I agree that in this context, you'd translate it by fan, obviously.
Poor band! ... typical of many new start-up bands here in the U.S.
What makes it plural?
It's common in Korean to leave out the plural marker (들); plurality is usually assumed/determined based on context.
Because it doesnt make sense if it was singular
Because if a band does not have one fan, neither do they have many.
In english you could say "he doesn't have a brother" or "he has no brothers" and it means the same