Was this your first time playing at Borgata, or your first time in a while? Have you recently significantly increased your play levels or have you in the past had stays where you've gotten many fewer comp dollars per stay? In my somewhat trial-and-error experience of observing how my Borgata comp offers evolve after each visit, I've noticed that they definitely use a per-trip averaging method, so if you had a few much smaller stays in the past, those may still be dragging you down even with this big stay on the books. I've also noticed that there seems to be something of a "history" effect, in that even if you play roughly the same amount each time, you get slightly better comps over time--so perhaps, as foolish as this may be on their part, one big trip might not be enough to get you fully in their good graces (though to some extent I may also be confusing this effect with the averaging across each visit effect).

They may also be discounting your play somewhat because of how long you spent at the hotel; certainly it's logical to think that someone who does that many comp dollars while staying only one night might be considered more valuable to the hotel than someone who has a room for several nights. So maybe you're getting rated more like an 80 comp dollars per night player, rather than a 400 comp dollars per trip player.

Or maybe it's something else entirely, these are just some ideas. The casinos must love how, with their opaque rewards systems, they get us running around like trained monkeys trying to figure out which is the right button to press to make things come out.