But banks are not in practice limited by reserve availability. A central plank of modern central bank dogma is control of interest rates which is significantly exercised through liquidity loans to banks in order to satisfy their Basel III obligations. That policy goal necessitates free provision of such loans. The reason deposits are desirable is because it's cheaper for the banks to borrow their liquidity from punters than from the inter bank market or from the CB. I guess in some very roundabout way what you say holds some water, but deposits certainly do not limit the ability of the bank to make loans, which is in truth limited by the availability of credit worthy borrowers.