You are right. When I used to review songs earlier, I usually went on talking about the bad things a mix had. However, due to the desolation growing around, I decided to stop doing it. Simply restricted myself to mixes I really like.
Besides, when I see someone doing it, artists generally do not like reading this kind of comments, because they think they are perfect and their point is above everyone's else opinions. So some of those people stopped writing this posts because they're not taken seriously. Laziness is something, but it is not the core.
And now that the standards are higher, less actual feedback will come. Few people really cares about improvement; since they get posted on front page, fame is what actually matters to most.