alt Hacker NewsI think it's mainly because they aren't forced by regulation.
Germany is another first mover with decades old banking systems and standards. German banks also dragged their feet supporting SEPA Instant or they added additional fees so that barely anybody wanted to use it.
Then the EU stepped in with regulation: If you support classic SEPA transactions, you also have to support SEPA Instant for the same price (which is almost always free for retail banking accounts). And suddenly banks did.
Yes, this could be fixed with regulation -- but whoever did the regulation would have to contend with angry fools complaining about how "the government took away my credit card rewards!!!" for years and of course the credit card companies themselves would stir and amplify those voices as much as possible.