The US is very spread out in a lot of places and geographically diverse. Many local routes cover a very large area. Currently, these Grumman vehicles only make

The US is very spread out in a lot of places and geographically diverse. Many local routes cover a very large area. Currently, these Grumman vehicles only make up 75% of the fleet. They also use vans, some electrics and in some areas they need 4x4 trucks and even boats. Considering the extreme punishment these vehicles take, i think the investment is probably worth it. I remember reading about how much money they spent on these Grumman vehicles decades ago and being appalled. But here we are 20 years later and they are still using those same trucks. The USPS is an order of magnitude larger than the swiss postal service. At some point it usually becomes just as cost effective to order a fleet of custom vehicles rather than off the shelf ones.