Congress directed the Fed to create FedNow so the largest commercial banks couldn’t gate smaller regional banks access to real time payments via the private consortium The Clearinghouse (owned by the banks you list). FedNow directly competes with this private network. Think what IRS’ Direct File is to TurboTax, reducing unnecessary economic drag at scale.

Those listed(and many others) support RTP, which came first and accomplished the same thing. They probably see little incentive in adding FedNow any time soon.