Banks need liquidity funding (including deposits) because they lend, not to lend. It’s actually an extremely important distinction to understanding money and debt (which neoclassical economics tends to, because they assume it all balances out so they can just ignore debt - it’s called the ‘loanable funds’ model and the fact that loans create deposits means it’s dangerously wrong).
Loans and deposits do not have any other direct connection than handling them together being a convenient and sensible way to handle things. You can make a loan without making a deposit (by asking bank to pay the loan out in cash) or bank can make a deposit without there being a respective loan created (E.g. bank paying dividend to shareholder account)
Further, if the banker is really dumb, bank can put money on the account with no economic reason whatsoever by just stating that I owe now to this customer a million dollars. No loan needed. But usually, of course, bank wants the customer to pay the money back, i.e. make a loan agreement.
Also, if the customer is really dumb, he can obviously "take a loan" and promise to pay bank a million dollars in a years time without ever receiving any money on any deposit account. A loan created without any deposit activity. Of course, usually when a customer agrees to pay a million dollar in a years time, he wants to get the money first...
