Why do banks delay on short sales?

[Chris Low]

Just curious why banks can take so long to make a decision on a short sale? What are they waiting for? We have a property under contract that is a short sale. We made the offer on 11/10 and the seller accepted it. It's been 18 days and we've heard nothing from the bank. I know this is common, so I'm not sweating it, I'm just wondering what goes on on the bank's end?