I think this is because historically, wire transfers between most banks in Germany have been easy and cheap for decades, while it is different in the US, as I understand it.
Interestingly, Citi has a nice web interface for person-to-person ACH transfers (direct deposit), but it's not widely used and I don't think most other banks have it.
It would be impractical to use this for most payments because the recipient has no indication that the transaction is actually going to take place until at least the next business day.
When individuals buy from merchants in the US, they almost always use a MasterCard or Visa (sometimes attached to a checking account, sometimes to a line of credit) via magnetic swipe or by typing the number. Individuals settle with each other individuals (tutoring, babysitting, reimbursing tickets, etc) using paper checks or cash.
I believe there are some startups targeting person-to-person payments, but most involve transaction fees and/or or creating an account with your banking details, neither of which anyone wants.