Human psyche. We tend to not judge people by their actions, but actions by their actor. If someone you like tells a joke, you'll find it funny. If someone you hate tells the exact same joke, trust me, you won't.
It's the same with levels. Agama could upload something mostly average and everybody would be like, "well it's not THAT superingenious but THAT and THAT and THAT totally rocks about it so 9.5!"
If someone who hasn't done well before uploads something nice, they get encouragement. And when someone seems to be bragging about how good they are, many people will see the need to point out their flaws because they tend to not like show-offs for some reason.
Yes, the last point was a hint at Impressive Creations. I'm sure your levels are awesome, and if I still played JJ2 ( which may soon happen again ), I would really look forward to playing some of your announced impressive creations.

But yeah, in the end, it all boils down to who seems nice to you and who doesn't. Just like how you probably found that post obnoxious.