But that's actually not true though, it takes days to settle those transactions, the payment processors just provide the illusion of instaneousness by smoothing it over with their own fungible cash reserves.
In the US the reason we still have T+2 is that it benefits the financial institutions to do so at the expense of the individual. One of the many reasons I have zero empathy for the industry.
Again, we do this in other areas where consumers demand it.
Yes, I'm really saying there are no downsides. Can you name one?
The question is: why? There's absolutely no technical (e.g. nightly batch processing) or process (e.g. physical cross-country mailiing of paper stocks) reason any more. It's 2021 not 1960, technology should have evolved over the last decades. To wait days for money and stock transfers is ridiculous
legacy systems. Someone in another thread mentioned a lot systems still use the "move file to this ftp folder and we'll process it in the morning" method to process transactions.
Other countries didn't have as much infrastructure to upgrade, and have been able to leap frog the US in many ways.