I think it probably makes a lot of sense when you think about the cost to the government to process individual personal items vs. a shipping container. I'm not sure where the cutoff is for it to be worth a customs agent's time to collect duty on individual private shipments, but when I order $100 worth of service kits from overseas, it's *definitely* costing the government more in customs agent salary (let alone facility costs, accountant salary, and banking costs) to get $10-20 worth of duty from me. If I had to guess, I'd bet some previous administration had an economist do the math and figured out the juice wasn't worth the squeeze on individual packages wort less than around the $800 mark.
Not saying it makes sense from a logical standpoint, but from an economic one, it may well.