The FDIC operates on a few constraints. One is that is has two roles, both as insurer, and as receiver. The second is that the law requires it to deal with fail

The FDIC operates on a few constraints. One is that is has two roles, both as insurer, and as receiver. The second is that the law requires it to deal with failed banks in the manner that incurs the least costs on its fund. It should be quite unsurprising that if an offer to buy 100% of the banks assets and liabilities comes in, this is likely to get accepted, since it likely to have the lowest possible costs to the FDIC itself. No costs in insurance reimbursing, obviously, but also fairly minimal receivership costs, as they don't have left over assets to sell, don't have to deal with creditors for any debts that transfer with the sale, leave a relatively small set of creditors (including the shareholders) to deal with. Whole bank purchase offers are not exactly rare, but offers to purchase only some of the assets while taking on some of the liabilities (often including accounts either in full, or up to the insured limit) are probably even more common. This is obviously more expensive to the FDIC, since they may end up with more unacquired liability (i.e. more creditors to deal with), assets to sell, etc. The FDIC does move fast, like disturbingly so, but their requirement to minimize their own expenses basically requires it. They generally already have the acquisition offers in hand when they first show up, and for their expected plan of action, have already talked with the relevant state regulators to have them ready to issue any approvals needed. Even things like issuing checks if no-one acquires the accounts, taking any more time than necessary can accrue additional costs. For things that don't actually cost the FDIC itself any money, like negotiating terms of acquisition, they can afford to be extremely consumer friendly. Requirements on the acquirer for things like keeping all branches open for at least x months, no sweat off the FDIC's back.