I mean, it doesn't even necessarily have anything to do with "corporate", it's just basic business. There will be lots of people in the area ringing in the new year at their timeshares/condos/whatever, so it makes sense to stay open during the day, but I'm sure they've done their research and are guessing that most people will want to be either "home" or at a party in Branson for the actual countdown.
I'd like a party at SDC, and would be very tempted to go, but I'm betting that if they tried that they would get maybe a few hundred people there. That's enough for a nice party, but it's absolute peanuts for a giant theme park like this. Just way more effort than it is worth. No one wants to be leaving SDC at 12:30 or 1AM to head back into Branson on New Years with all the drunks running around.
If they had a resort on site, then it would make more sense.