It really is not, and I would assume less 1% of consumer purchases are done using a bank tranfer / account number.

In Germany (2021), online purchases were paid by:

   33% Bill & bank transfer
   20% Direct debit
   20% PayPal
   11% Credit card
   16% various others

https://www.handelsblatt.com/finanzen/banken-versicherungen/...

Imagine you are an sized e-commerce merchant. Someone checks out on your website and sends you a bank transfer. Then what?

You go through your ledger (bank account), find the transaction with an order ID as a memo (hopefully the buyer added it and correctly), and then you look up that order in your system and submit the order form to your warehouse?

It works like: customer gets an order number and puts this on the description of the bank transfer. This is parsed by the accounting SW coupled to this bank account, and voila!

Most banks charge some amount per transaction on commercial accounts though.

The problem is that it's extremely failure prone and not instant.

Gotta wait for the buyer to make the transfer, you gotta wait for the transfer to go through, you gotta hope that the buyer put in the order number in the description.

Well, it really doesn’t suit itself for automation, much less for real-time transactions. Say, you want to sell access to an article on your website. It would be cumbersome for the customer to have to switch over to their online banking and typing in all details (ok, today we have QR codes, but you still need to jump through many hoops, much more than with, say, a credit card or PayPal payment). Then it takes time until the money shows up in your account - sometimes several days. And, finally, there was no API access available from the banks for small sellers that would have allowed them to build an integration, even if they had the resources to write custom software.