They were running out of supplies.
Amelia accepted the newcomer easily when she came downstairs from the 12-hour power nap she had been taking because of her tendency to stay up for 30 consecutive hours with no rest. So the result of such sleep deprivation was binge-napping. Everyone (‘everyone’ meaning Annalise, Emilio, and Constance at this point) had just decided that as long as it didn’t interfere with their survival it was fine.
But when Amelia came downstairs for her just-came-out-of-hibernation meal, she had announced it to the group at large. It was a simple, unavoidable fact.
All forms of government and law enforcement had dissolved at this point. It was every person for themselves.