I think your take is a little extreme being that currently there are tools available to create your own "aram section." Just search aram and specify how old the discussion can be and boom.
Really though this is more work, its less dependable and maybe most importantly I think people who would post won't only because they ASSUME no one will read it anyway.
Im saying I think its true Riot is damaging those communities by not more fully facilitating them, not even acknowledging their existence. When you think about it though it seems reasonable for them to not want to create competition for their own game. If ARAM became the standard mode how long before another company comes up with a game designed around that single mode. Now there is a whole, single community primed and ready to move on to this new game. Scary when you think about it that way if you are Riot.