I don't see why people shouldn't expect comments on their work. This place is, first and foremost, a forum. A forum's goal is to socialize; specifically, in this case, about LoL. The type of content varies, but it should be expected that posts should get comments; to expect otherwise means that the forum as a whole, is pointless.
In the case of champion concepts however, I think the problem stems more from downvoting and the lack of communication between actual concept creators. In regards to the former, champion concepts seem to be consistently downvoted without adding meaningful discussion for why they are downvoted. This prevents any discourse from being held from what might be genuinely interesting ideas. Unfortunately, there's not much we can do about this problem, so we'll just have to take it as is. The latter problem may be that concept creation is very unique niche in the forum itself. As such, the audience to whom champion concepts might appeal to are largely comprised of other concept creators. These people are the bulk that both want feedback for their own concepts, and want to facilitate discussion about other concepts. If so, then such creators need to be more proactive in commenting on other people's work, in order to create a more unified community concerning LoL champ conceptualization. The audience isn't the people who simply come here and go out without commenting (possibly because champion creation isn't as interesting as other topics such as skin ideas, balancing issues, etc.), but other content creators who themselves have their own concepts. In which case, it might be better to encourage more commenting among champion concept creators rather than the general audience as a whole (I think one of these ideas in action is the CCOS monthly contest, which is pretty cool).
Anyway, this is just one weird long rant about this topic. I might be super wrong about my analysis though, so take it with a grain of salt.