I have to agree with some of the posters on here that if all the PA was there, surely someone from either of the three bands could have sorted out something sound wise to allow all the bands to play.
A basic set up would have carried things through, instruments through the back line and just use the in house PA for the vocals, simples.
The only thing I can assume that stopped the gig, was the venue owner probably didn’t want anyone other than the usual sound person touching the equipment.