People expect a food bank to feel solemn. Mostly it is a warehouse, a kettle, somebody's terrible playlist, and a running argument about the best way to stack tins.
The enjoyment is real and it is not noble. It comes from the same place as any decent shift with decent colleagues: being useful, being busy, having a specific job that finishes at four.
That ordinariness is worth protecting. Help offered from a great moral height tends to be felt as height. Help offered by somebody who quite likes being there on a Thursday is a good deal easier to accept.