Riot will never react to champion concepts, nor will they ever (openly) use them. They have said multiple times that they can't do that because of legal reasons. I'm sorry, but thats just how it is :/
lack of attention from the board itself is another matter...My concepts usually get some attention, some more then others. It all depends how you spread the word about it. I always post my concepts on a local league of legends facebook page and that always gathers a lot of attention :)
The quality of the concept also matters. Is it a unique champion? Does it have interesting mechanics? Is it an interesting theme? Does it have a catchy name/title? In my experience, the more agressive/gritty concepts (or dragons) get the most attention. I once made a very interesting concept of a traditional fairy champion, but nobody was really interested in it...So it all depends on what the boards want and the quality of your work :/