If you are asking why it happens, it's because it's fed from the No 2 galley bus which is one of the first items to be shed when load shedding is required. If you're asking why it's fed from the galley bus .... well, that's one for the guy who designed the electrial system!!
Note that the 'old chestnut' 400 question of "what indications are there of electrical load shedding?" is usually answered as "None", meaning no ELCU messages, becausethey're inhibited. Of course, the correct answer is that if it goes deep enough, you'll get various fuel pump messages starting with FUEL PUMP 3 FWD, then FUEL OVRD 2 FWD etc.