Because Riot has been forcing their own idealogy onto the game for several years now, so this caused some sort of general negative feedback from the community, so they are plainly and simply ignoring anything that they don't agree with.
They've been slowly moving League of Legends away from the concept of "game" to bring it closer to some sort of sport, visual entertainment and generic popular universe. They also forced a meta based on their favorite playerbase, AKA eastern China and Korea, to drain as much revenue from the game as possible.
This is generally not very welcome amongst the community, and this includes the gameplay boards, that some Rioters consider (I'm not even exagerating anything) as utterly useless, the reason behind such statement being very unprecise, but we can believe it is because the playerbase disagree with the direction the developpers has been utterly FORCING the game into, so they are basically blocking their ears like children because they don't like whats coming from the community.
This doesn't even limit itself to the gameplay boards: Riot and its employees have been avoiding anything that is conversation on balance with actual players, only making statement on balance from what THEY personally think about the game on their personnal twitter accounts. Some months ago, a Rioter started duoing with Hashinshin while discussing balance. The Rioter gave minimum feedback on balance conversation with Hashinshin and we pretty much never heard again of anything that could've be the consequence of this encounter and not a single Rioter did a comparable action ever since.
Some people here might argue that they are ignoring the boards because of the toxicity and the unviability on the feedback here, but this is just a bland excuse since actual feedback does exist here and developped discussion about balance existed back in the day where the game was mostly appreciated by everyone (AKA barely anyone would give feedback on balance compaired to what its like today). Those who does agree with riot abandonning any gameplay-related relation with the community will also tell that people who complain are salty because of the state of the game, which is highly ironic (and, frankly, also quite moronic if I say so) since their arguments are only justifiable by the fact that they are salty themselves about the fact that some people do care about having a balanced game rather than something they can abuse with meta or cheesing.
So, TLDR: Riot shifted the game into a direction a lot of people disagree it, but they want it to stay this way so they willingly ignore the community because of it. This causes also a vocal portion of the community to protest against people disagreeing with Riot, this certain portion having few and shady arguments who are pretty much all variations of "people are salty and I'm not lol"
