When the interest rate was zero they could borrow infinite overnight funds for nothing. When the interest rate is 3.75% it stops being a free facility. Also, post COVID, the Fed was flooding the economy with cash and market participants actually had the opposite problem: they were coming to the reverse repo facility (https://www.newyorkfed.org/markets/desk-operations/reverse-r...). That flood has subsided, so repo activity is returning to pre-COVID norms.

Despite the tone of the OP, the people who exchange securities for cash at the repo facility are paying not just the fed rate, but a higher punitive rate. It is expensive, by design, so banks seek liquidity deals privately if they can. It is not, in any sense, bags of money from helicopters.