In the United States, at least this is partly because money is transferred through ACH , and it is more efficient to calculate which banks should, in which banks in large, overnight batches, than for individual transactions. Although authorizations are often real-time, they do not have to be, and it is still a "stand-alone", batch system at its core. It was designed at a time when online was not possible, and that is how it works.
Technically, you can close the package after each transaction, but each time you pay a commission for this, because the calculation takes the actual work, and not how the network was created for use. And you still will not receive money until the next business day in the near future due to how ACH works.
This contrasts with EFTPOS (online debit card transaction in which you enter your PIN code on the terminal), which includes various technologies, different networks and immediate transfer of funds.
In the USA, as a rule, for debit cards you can also brand a credit card network, such as Visa or MasterCard. When you scroll through these cards and enter the PIN code, it goes through the EFTPOS network (Interlink, Star, Pulse - you saw these names on your cards before, but probably didn’t think about it). This is usually beneficial for merchants, because fees are lower, and the issuing bank is usually responsible for fraud (all this happens online in real time, and the user is authenticated using a PIN code). When you hold these cards and don’t enter your PIN code (sometimes signing a receipt), then it goes through the credit card network - again, a completely different network - and is part of the night party. The merchant usually pays a higher fee, and if used fraudulently, the seller usually ends the account. (The buyer almost always passes it to the seller). If you ever wondered why Walmart or your grocery store by default downloads a PIN code and forces you to jump over hoops to find the Credit function, therefore, debit is cheaper for them. And if you ever wondered why an e-commerce store is causing you trouble when your billing address is incorrect, why? If you dispute a transaction as fraudulent, it is those who pay the bill and then do not sweat the bank.