Because they are neither low mileage and the medical equipment behind needs power. You never want your battery to go flat in an ambulance and lose the mobility and life support at the same time. Also, they're used the way EVs hate most. Accelerate and decelerate constantly while trying to plow through traffic in city centers and rush hours.
> fire trucks Would be excellent EVs. They have super low millage...
I wouldn't want an inextinguishable box of lithium near something hot like a fire. Would you?
> power company trucks [are] Excellent option for EVs because they almost never haul equipment
I don't know how yours operate but the power company trucks I see carry a whole workshop behind, and some of them carries enough spare parts to build a sizeable transformer from scratch. If we are talking about cranes, their hydraulics will consume enough energy to affect their mileage considerably.
> Generators are a thing that pretty much every one of these services will have.
You'd need a couple of 1.2MVA generators to charge these vehicles if you want to do it quickly, with redundancy. And these things are neither small, nor silent or can be deployed anywhere you like. We have a couple of them outside, and boy, they're literally shipping container sized things. This excludes the fuel tanks and other infrastructure they need to be able to generate electricity.
> And, consider this when thinking of a "grid down" situation. How do you pump fuel if the grid is down?
Uh, just pour fuel to the tanks or pump with a manual pump?