Why couldn't cruisers redistribute anti-aircraft ammunition at Crete?

Why couldn't the departing cruisers transfer anti-aircraft ammunition to Fiji and Gloucester?

The departing ships were still under threat and needed their ammunition, while an at-sea transfer would take time and expose both ships.

Cruisers returning to Alexandria still faced air attack and needed ammunition for their own defense. Giving away their remaining anti-aircraft rounds would leave them more vulnerable during the withdrawal. Transferring ammunition between ships at sea would also take time while both ships remained exposed. The returning cruisers therefore could not simply hand their remaining supply to Fiji and Gloucester.