Maybe I'm a bit to naive since I don't know the US banking system, but at least in the EU you just need to tell someone your IBAN and Name and they can transfer money to your account. Is it that much harder in the US?
Yes, you can get wire transfers or ACH at most banks with a routing number and account number. But wire transfers usually cost money to send, and sometimes cost money to get. Generalized ACH transfers usually come through a service provider, and that costs money too.
Also, the same numbers can be used to credit and debit an account, and also to forge checks. So giving your payment credentials (or writing a check) is a security risk. I'm a little fuzzy on details, but someone at my employer at the time (Facebook) had my payroll data on a device in a laptop bag that got stolen in San Francisco, and as a result I had to be hyper vigilant on checking for unauthorized transactions (or get a new account number, but that's more disruptive, assuming the theft was just normal SF theft, like it probably was)