The point is to not stick out on a cursory glance. As you drive by you see a bunch of green, you might notice there was something up with that particular tree, but that’s it. A plain cell tower would stick out from a distance, interrupting the natural view.
It’s like those mirror covered buildings that reflect their surroundings, giving the impression of unbroken landscape as you drive by. They’re not invisible, you know there’s a huge building there, but it’s a hell of a lot less disruptive than a regular one.