They could use tugs to free up a few A Gate slots (swapping with C), park the last arrivals at A Gates then either send them off from the A Gates in the morning or use the 7 hour window to reposition a handful ~5/6 between A/C.

They won’t do so because ultimately it’s a cost thing isn’t it? AND you will get inverse criticism:

”WHY do BA already make me get up at the crack of dawn only to send my 06:05 Frankfurt flight off from C Gates? Don’t they realise I don’t want to book an overnight hotel and…”

It’s also true that you can’t please all of the people all of the time. There’s one cake and however many slices I cut it into there is still only one cake!