Criminals just use stolen identities (from breaches of KYC data).
But in reality it was the right that was setting us up for failure all this time, going back to at least Reagan as California's governor reducing funding to schools. Then Nixon doubled down.
ACH clearing (transaction information) happens multiple times per day. Originating bank sends a list of transactions to the clearing house, Receiving bank is notified of transaction pending.
ACH settlement (bank-bank funds transfer) happens overnight. Funds from the Originating bank are "rehomed" to the Federal Reserve, and then again to the Receiving bank. This is, obviously, a database update.
ACH posting (funds available to customer) happens whenever the Receiving bank feels it's appropriate. Generally, by local close of business on the settlement lot schedule (same day or next day). The receiver may choose to delay posting to customer account if they don't trust the Originator, or the customer, or just for fun.
ACH transactions are reversible. This is the reason posting happens as quickly as it does (!), but also the reason posting takes as long as it does.
You gotta understand, there's the law, then there's enforcement of laws, then there's punishments for getting caught breaking the law. The banks have done the math. Maybe they've even lobbied to have the penalties/enforcers reduced. It doesn't pay for them to follow this law strictly, so they don't. You'll find this across the legal system. It comes down hard on the poor and marginalized, but gives a lot of grace to the rich, even if at our expense.