Part of this is habit, and part is convenience.
The way traditional Accounts Payable departments work is as follows:
- The buyer creates a Purchase Order, this is entered into the accounting
system and mailed/emailed to the vendor
- The invoice arrives from the vendor, this is received by the AP department and entered into the
system.
- The AP department checks with the warehouse to make sure the items arrived. This is either a physical slip of paper, or is entered into the accounting
system by the warehouse.
- Once all three parts of this match up, only then the invoice is scheduled for payment. Most companies are not going to pre-pay you for items. Too much risk, and too much cash tied up.
- Most AP departments run checks once a week, once every two weeks, or once a month. You'll probably start to notice a pattern as to when they arrive. The reason is, they can just take the list of all the invoices that have been approved and matched in the previous steps, and click "print."
- Most large businesses won't pay you by credit card. The amount of time it would take them to go in an enter credit card information for any real number of vendors would be ridiculous. Printing and mailing checks is substantially faster.
In the US, we haven't really caught on to ACH payments en-masse yet. A lot of times, you have to go into your bank account to schedule them. It's substantially faster to just pay by check.