The debate over bank reserves, primary auctions, and secondary markets injects some confusion in the talk. The main reason new Treasury auctions are better than secondary market purchases, both for banks and for non-banks, is that transaction costs are lower. Dealers in the secondary market impose transaction costs via the bid-ask spread.
When banks earn interest on reserves, the rate tends to be higher than T-bill rates, meaning rational banks don't want to hold T-bills as alternatives to the higher interest earning reserves at Fed. Primary Dealers are expected to "pay the tail" in a weak primary auction. The Fed ensures that there are always sufficient bank reserves to clear payment for Treasury auctions by doing repo with Primary Dealers or other firms who hypothecate existing Treasuries or other assets to obtain reserves when necessary for clearing the new Treasury auction.
Joe