I'm sure some old fart thought you couldn't run big motors on a UPS because of the inrush current, whilst also being ignorant of the fact that all the new machinery runs the motors on VFDs so there's basically no inrush current.

The problem is the harmonics utterly fuck with the ratings on the UPS on most LV stuff, and by the time you start pushing into MV and getting 12 pulse rectified VVVFs with dedicated transformers the loads are too big to even try to put on a UPS long-term anyway.

You might be able to get away with a few 10's of kW on some HVAC rack somewhere or what not but really your UPS is there to keep coms, controls and you protection/relaying going while you start the backup gens.