This seems a regular occurrence in North America, where handling agents are somewhat lacking compared to the services they can supply in Europe; airlines seem to self-handle to a greater extent there, and come a diversion things all fall apart. This applies right through to use of gates, and everything else. Presumably when the APU shut down there was no agent able to hook up a generator. I bet the toilets stopped working as well.
It shouldn't need regulating, but the level of indifference shown by head offices unfortunately seems to show that it needs to be.