The reason the fed lowered the reserve amount to zero is because it was no longer a real barrier to lending. Since 2008 US banks had amassed something like 4 trillion in liquid capital and were lending at the same or reduced rates. There was also a currency shock due to the pandemic. The search term is “ample reserves regime”.

The fed still has other requirements for use of their facilities and every bank that lends money is covered by a wide swath of regulators that have their own asset to liability and loan makeup requirements.