OK so as a none techie why is it not genuinely instant? Why can't my cash be exchanged for the stock in real time (where real time is defined as within a minute or two say).
https://www.fintechfutures.com/2013/03/moscow-exchange-adopt...
Also, you may still be able to pay for stocks with checks at some places, so the cash isn't always available.
The US banking system is arcane and archaic. It's cheaper not to modernize to be sure. Forgive me for being frustrated at banks cheaping out on this when they average quarter of a trillion dollars in profit every year over the last few years.
I routinely pay street vendors directly from my bank account to theirs for 10¢ transactions .