Banks are highly regulated in exactly how much of the deposits they can use and what kind of risks they can take with it. This is complicated: https://en.wikipedia.org/wiki/Capital_requirement

Also in the US at least banks are FDIC insured, so if the bank is breaking the law and gambling inappropriately consumers are still protected.

"How is crypto different than a bank" is a reductive and foolish comparison. There are many, many differences. The primary one being that almost every cryptocurrency system is a fraud at its heart.