To send a message.
Can you imagine what you can do with thermite to those cars?

Aim for the fuel tank then.
But even without a sound made by the thermite, the message can be loud and clear.

https://en.wikipedia.org/wiki/Thermite
Doesn’t remove the cars, but sends a loud message.

Unions are the compromise.
If the compromise gets abolished by the corporate overlords, give them what they deserve.