Honestly, it makes perfect sense fo the USPS to go with a "low-volume turd": they apparently don't want something off-the-shelf, they want something custom for their unique needs. Who's going to build this for them other than a government contractor? You mention the Ford Transit, but the steering wheel is on the wrong side and it probably has some other problems since it isn't specifically designed as a mail truck. You might suggest here that they could contract with Ford to make a custom version, but look above at what I wrote: most companies have no interest in this, and will simply turn down any government contracts, and I imagine Ford is the same way. Why deal with the hassle? For most companies, it's simply not worth it, otherwise they would be actively bidding on government contracts. So a Ford vehicle probably simply isn't an option here, and the USPS's only options are low-volume turds made by defense contractors.