Because there's no serious answers being given even though there are at least 2:
- trees have roots, roots ruin any nearby human infrastructure. You'll note this says "in urban environments" and that there are trees nearby, so this is probably the big reason
- trees need maintenance, which costs money. this is a stupid reason imo, but it's one nonetheless
- algae is cool, ok?
Another reference, this time in 3D:
Me, 6'4" 235lb, that's a full grown and a cub 1:1 statue