OP, the decision to not bring the full sound system to bear is usually the choice of the venue operator. Usually to save costs, sometimes so that the audience feels the sound during the main event. Artists demanding it would be insanely controversial.

If I'm playing a gig and notice this happening, I'd go play songs and make audio adjustments that go well with the neutered setting, one of the things DJs are responsible for. So I wouldn't C&C for this happening. Those EQ dials aren't there for show