Cabin crew usually don't set them (although they may on certain aircraft types, and I wish they did!) In fact the cabin crew are only seated near the doors for a short period during take off and landing. Normally they are very active and working in galleys. Generally they request cooler temperatures for these reasons.
By that comment, it would appear that you are a shorthaul person.
What we are talking about here is long overnight flights, by definition longhaul flights.
On these flights the cabin crew spend a lot of their time inactive by doors while the passengers attempt to sleep, after the service is complete.
The flight crew set basic temperatures which are then varied by cabin zone by the cabin crew. In my extensive longhaul experience, they usually complain during the service that the temp is too high (often as a result of inadequate cooling capability on the ground) and then after the service ramp the temps back up from the achieved 21-22deg to 25deg after the service when they themselves are inactive.