For a MTY flyer, it makes sense. Why? This was my schedule:

Take the 12am bus from MTY bound for San Antonio-- the bus arrives the border, everyone clears security when there are no lines, and the bus continues to the station where taxis are waiting. I took a cab to the airport, had plenty of time to check in, etc. (security didn't even open until 20 min. before departure), made my connection in IAH, hopped on the Metro at DCA, and I was in my office by noon.

Let's replay this some... I was hanging out with friends in MTY until late Sun when they were about to go to sleep, then I just slept on buses/flights, made the requisite tranfers, got into DCA 11 hours later with no en route delays, and only used 4 hours of vacation. Sure, I slept a lot that night, but on Mon. AM, all worked out.

So why a midnight bus to LRD instead of MFE? For the same reason airlines fly red-eyes SFO to the East Coast and not SFO to SEA: you just don't have enough elapsed time to make overnight schedules convenient on MTY-MFE. Being generous, it's a 3 hour trip. So, either you're leaving at midnight to arrive 3am, or you're leaving at 3am to arrive by 6.... who would want to choose either?? For MTY-SAT on the other hand, buses leave MTY at 12 midnight to arrive SAT around 7am, in time for the new workday... the LRD stop is intermediate. Thus, when I booked the reservation on the fly (literally on my cell _while_ standing at the NW DCA counter), I chose to return from LRD instead of MFE without knowing bus schedules for sure.