First, there is not, so far as I can see, a STAR for either of these airports. Not sure how SWA SOPs would program for that situation - direct to the airport itself?
The routing given by flightaware.com is ACITO ADELL AKMIE ARLYN STL MAP DGD.
https://flightaware.com/live/flight/...145Z/KMDW/KBBG
I would certainly at least terminate it with KBBG in the box with a discontinuity for a mileage and fuel crosscheck but some folks leave the endpoint out until the actual runway and approach is known. And others would omit the discontinuity and have DGD direct KBBG as the last leg in the FMS.
These different ways of programming the box are considered to be in the realm of technique where I work, at some places they may be overridden by SOP.
And, there are subtle differences in the ancient cryptic user interface on different models of FMS I've flown with over the years. Rather than simplify the user interface, many training hours are spent with wacky route mods and tricks that work on some boxes but are gotchas on others. Many 'modern' aircraft still have FMS's with memory measured in megs, not gigs, and databases will be missing some waypoints and approaches to get a region to fit into the limited memory.
Once I figured out that we would probably be landing on 14, I'd select the RNAV (GPS) Rwy 14 approach in the box even if I planned vectors to a visual. It would give advisory path guidance for the night approach with no PAPI's or VASI.
As Huck speculated, one possible scenario is that the crew were set up for the ILS 32 and switched to the visual 14 late and decided not to mess with the FMS down low. Seems like years ago places like Air Canada had a policy that you wouldn't change anything in the box below 10,000 feet and instead rely on raw data if you had a runway change. Unfortunately, these RNAV (GPS) approaches don't have a lot of raw data.
Southwest certainly has a traditional reputation as a raw data, round dial, hand flying, no VNAV, visual approach airline. Kinda like Piedmont back in the day with the V1, Rotate taxi speeds.