It's primarily a regulatory problem with how the US financial system is set up and overseen by the Federal Government. It's a hyper regulated industry. Trying to do anything even slightly different in the world of moving money, banking, finance etc is simply a nightmare.

Payment innovation would have been drastically faster, were it not for the obscene regulations that are in place at both the Federal and State levels. PayPal ran into this brick wall while traveling at a high rate of speed, very early into its existence.