I'm wondering if these cars were attacked because they look "modern" and the perpetrators thought they'd get out and about, showing their handiwork to fellow morons.
My experience is that this is the incentive to attack railway vehicles.
At our museum, we had a number of attacks, but nullified them with the following sign:

GRAFFITI
1. This is a museum. It is not part of "the railways"
2. All graffiti is removed within hours of application.
3. Nothing leaves this yard with graffiti on it.
WHY BOTHER?

The signs were illuminated with solar LED lights and for some time, we also had volunteers do visible patrols at night.
I also arranged to check the yard every morning on my way to work and had a list of people I could call if we had an attack.
We haven't had an attack for about 5 years, so it worked!
Cheers, Bob