National banking players did not want to give up their turf. The European Union had to twist their arms to get them to agree to SEPA transfers, instant transfers, etc.
If banking players cannot agree, then regulation (or the threat of regulation) must be used.
I once worked at a company doing payment card personalization (its the company who turn blank smart cards into finalized cards on behalf of banks. They print the customers names, emboss the account number, and program the chip and the magstrip)
Every year they had comprehensive security audits from Visa, Mastercard and Groupe Carte Bleue.
One guy there told me that they did the Groupe Carte Bleue audit first, because its the toughest. If they passed it they were sure to pass the others.
Trump sure has moved the needle on that! We used to pay protection money to the US via this. Now we don't get the protection, so we don't need to pay.
VISA and Mastercard never resolved major technical problems. It's nothing a bank wouldn't already be able to achieve internally from a technological complexity point of view. They didn't invent any of the technologies, they just navigated the political and regulatory hurdles, then leveraged their position for more.
Your comment makes it look like the problems are "just" political or regulatory. These are more often then not the bigger ones.
Technology and some systems could be shared.
There are also business and regulatory problems with regard to international transactions.