Banks only keep enough cash in their vaults and cash drawers to meet the daily needs of the transactions at the bank.
Whenever you deposit cash into the bank they don't keep that cash in their bank forever or until you withdraw it or use it.
The cash is loaned out to other people or handed over to other people for their transactions and then excess cash is taken to another secure undisclosed location by an armored truck.
Most small banks keep at most $50,000.00 in cash on hand in their vaults and cash drawers combined while larger banks keep around $200,000.00 to $300,000.00
Banks invest your deposited money into stocks etc to earn money themselves which is how they make their most profit.