Lending is tight to a banks equity. Prior to Basel II (early 2000s) this was some 8% per loan. So the more equity you have, the more loans you can provide. As small regional banks are unlikely to have the same amount of equity than JPMorgan Chase, they cannot provide the same amount of loans.
Under the followup regime (Basel III) its: https://en.wikipedia.org/wiki/Basel_III#Leverage_ratio