as usual with any large-scale procurement decision, it is a whole lot of politics. the anti-EV people were pushing against it, the defense contractors that run the government had more experience in gas powered vehicles, and the environmentalists were pushing for impractical targets like 100% EV, which just gave ammunition to the people who didn't want EVs.

the cool thing here seems to be that practicality is actually going to win out, and the postal trucks will end up being EVs on routes where that makes sense, and internal combustion on routes where EVs don't make sense.