Did it ever occur to you that they have insurance to cover damages like this? The delay from small scale vandalism has probably set them back at the most what, 1-2 days?

Word of advice wait until said buildings are nearly complete and then gut them with fire next time, much bigger costs, substantially higher insurance premiums and excesses, and a much bigger delay.

If companies claim for damages on their insurance their insurance costs go up

talk is cheap.

It is true that arson would cause a greater financial damage, but it is more risky and the state will put more resources into investigating it. You are looking at a much longer prison sentence if caught, especially if it is politically motivated.

Pushing the insurance premiums up is a worthy goal but that only happen with sustained campaigns e.g. against the meat industry. It is the propaganda value of these actions that is the main benefit, and for that, many small acts of minor criminal damage are just as good as a few big arson attacks.