Because they have nothing better to do but nit pick and look for ways to spoil things for others when something like this makes no hardship whatsoever. You have to be bored to look and care about small things like this. On my mainland plot I love when a neighbour has nice trees overhanging without stealing prims. It looks natural however something like a huge wall or floating junk in the sky I can understand the need to get them removed. If something does not steal your prims, is invisible and phantom, who cares?