We do, it’s called FedNow, it’s been live for some time. Instant payments for a few cents per transaction, up to $10M per transfer. Why don’t financial institutions switch to it? To keep getting the fees they’re accustom to.
Other countries are working to avoid the US financial infra rake and grift, but you’re captured by it if you’re stuck in the US unfortunately, because the US political will does not exist to compress profits for the financial services industry.