[pishpash]

Because banks have much greater presence and marketing reach, being involved in a lot more of the ordinary financial transactions than just withdrawing cash. As only one example of this, brokerage checking doesn't have an obvious path towards insured savings vehicles, you'll have to do some research and have an investor mindset which most banking customers don't want to bother with. If you have a loan, it also becomes another account and institution to deal with, which if you're not an investor you don't want.