The type of tree for one. Replacing ancient forest will not keep the diversity. The effectiveness for two; round here they planted hundreds of thousands of trees to offset a new bypass, but it was the wrong time of year and they pretty much all died. Thirdly, why do it in the first place, when there must be hundreds of existing suitable venues? Fourthly, optics - it looks terrible and undermines any message they might come up with.
Anyone wondering why they are so needlessly cruel - that's the point. It's a demonstration of malign power for both the oppressed and the oppressors so that each knows their place.
Could be useful if you have a spray can that has lost its rattle.