It's owned by the bank because the original "owner" was in default or about to be in default (I can't recall which.) Not unlike the Fontainbleau, except in this situation the bank decided to take back the loan, finish the thing and operate the casino, as it would be better than walking away from a multi-billion loss.
In the long run, a bank does not want to be in the casino business. It's highly likely that they will spend the next two years building a customer base, partnering with a hotel (Marriott, as previously mentioned,) and then selling to an established operator once the recession is over. Make no mistake, Deutsche Bank wants their principle back as liquid assets, not a 3.9b liability in the form of a property. If they could find an owner now they would.
I do give them props for deciding to finish the thing rather than let it become another Fontainbleu or Echelon.
Lloyds could have done something similar with The M recently - Marnell wasn't able to make payments, but the lessor of two evils was to let him continue to operate it at a loss instead of the bank trying to own/operate. In the end, they decided they wanted anything they could get for it, and Penn ended up with an incredibly sweet deal for appx 25 cents on the dollar. That property was already in operation for more than a year, but the same issue basically: a loan that would work only in the boom days in 2005-2006, and was not set up for the Great Recession.