The possible issues of "saving cash" on the dockage upcharge for power; 50 vs. 60 cycle compatiblity; or there aren't enough amps of service available --

It is possible that the captain of the big cat know something about the quality of the power on the dock and is leary about hooking up. While I would neglect the issue in the marinas that I've visited ou might see if you have some issues with the ground being "neutral" or somehow electrolysis concerns may be leading the cat to be running its generator(s).

I've seen a number of BIG motor vessels that run their generators at the dock because they can't get adequate power. We have a whole leg of the Nantucket Boat Basin go out once when a guy had hooked-up to three shorepower connections and it blew-out the breakers. He switched to running one of his medium generators. It didn't bother us -- we were close to his bow, his stern was over a 100' away.