Not out of spite, but to protect the workers as they remove the trucks, which the article cited as a specific concern. It will have obvious ramifications in decreased value of the truck, but that’s an expected side effect of deploying it as a paramilitary blockade in a large city anyways.
Maybe I missed something, but the way I read it is that the danger is from the drivers and other protestors, not the trucks themselves. Disabling the engines would make it more difficult to move the trucks, not less.