I think it's because the tree is a public amenity. Like instead of just being a nuisance to a few people he destroyed something that's there for everyone's benefit. As much as there was a tacit acceptance of people grifting and stealing from supply lines and workplaces, stealing from or damaging public spaces was treated comparatively severely from what I've read. It was probably chosen for the poster because it's a shameful crime against the public without being something sordid or unpleasant to talk about.