I cannot answer that for them,they chose not to, did i say they could not?
why they chose not to when they must have known it was a club with certain rules, and accepted the gig, that is their business
however i am versatile enough, that i can do it, i started and did my first gig as an unaccompanied singer,
im my experience if one is going to sing the same songs that one normally does with an instrument they have to be practised unaccompanied.
so kenny , i do not need to have the rules of the club waived, i am comforable doing the gig unaccompanied or accompanied, however i will taker my faithful gadget just to take an occasional note for pitching