I had a few minutes and found that you can get to and from BWI-LAX on non-stops and direct flights coming and going that coordinate well with BWI PBI flights.

The best LAX-PBI build I could find using 4/2 was 1807 that arrives in BWI at 3:46. There is a 5:00 p.m. flight to PBI from BWI.

On the return using 4/4 were more options. The one I found 373 PBI-BWI arrives 10:15. BWI-LAX NS 676 leaves at 12:00. There is a later option using a direct flight with one stop from BWI that could use a later flight from PBI.

If you call and make your reservation, the agent should be able to put these together. It will work better if you do your research up front and can just say "I need to fly from LAX to PBI on (date) with a return on (date). I see for my first date that I can take Flight # XX to BWI and the Flight #XY to PBI. Can you put that together as a connection?"

What I do is I open the schedules for all four options in different tabs so I can move back and forth between them while talking. I would have LAX-BWI, BWI-PBI for my first date and PBI-BWI and BWI-LAX for my return all open so I can tell the agent what I see with times.

What I can not understand is why they would discontinue service with connections that are fairly easy to build.