Unfortunately, BUR doesn’t have any catering facilities. (Not that DL couldn’t double cater for the return from BUR, depending on galley space.) Before B6 closed the station, many speculated BUR-JFK could have been a great Mint route but for the lack of catering there
If they did cater the inbound, they would have to cater the inbound flight from SLC for the BUR-ATL leg. BUR-ATL departs before ATL-BUR arrives. The aircraft for BUR-ATL comes in from SLC while the aircraft that does ATL-BUR then does BUR-SLC though I'm guessing there are still issues if the aircraft were to be catered in SLC.
I wonder what AA does at BUR because AA advertises a meal in both directions between DFW & BUR (the 7:00 AM BUR-DFW advertises "Continental Breakfast" - the 12:34 PM departure advertises "Lunch" - maybe AA double caters from DFW for the afternoon flight).