Because the "prepper" never had to deal with an actual disaster.

You can stockpile diesel for a generator (unlike electrons). That's what actual prepping looks like.

Take it from a Ukrainian.

Diesel can't be stored forever. Maybe a few years with stabilizer. So you need to remember to rotate it out (and have some use for the fuel you're rotating out).

Much easier to just buy some solar panels to recharge the electric truck.

Diesel just lengthens the storage time. You still have to go somewhere to get it when your onsite tank runs dry. For the electric side you could also have a bunch of solar panels. Lots of choices.

And if the needle is so far towards apocalypse, then the horse beats your diesel. Repairs itself, refuels itself, and replaces itself.

That's fun till you run out. The sun isn't going to replace your daily use.