[Johnny555]

Sure you can make it a full hybrid but then you’re like 80% of the way there to a battery vehicle anyway.

But then you don't need to build dozens of charging ports at post offices that may or may not have the electrical infrastructure to charge a fleet of mail trucks every night

[MBCook]

It's a fleet vehicle. The government can afford it and it will pay off in spades over the lifetime of the vehicles.

Upfront cost doesn't matter nearly as much as lifetime cost. And the difference is not going to be small.