I'll be devil's advocate for Slimy Bankman-Fraud. A state bank charter is very hard to get in a hurry. In most states, the charter process can take years. Many firms like this acquire their charter by buying an existing bank, which allows you to assume their charter instead of having to apply for one.

Another big financial player that just went thru the same thing (merging with a traditional bank to gain a charter) is SoFi.