Why do Riot posters only answer to meme posts and not serious balance questions or gameplay issues?

They may not be allowed to. They may not have an answer. They may not want to based on general community backlash regardless of what they say. They may not be part of the department that deals with those issues. They may not be on the boards and they may actually be working. They may not want to answer a question that is likely to change and end up lying to the community.

Or they might just be dicks and don't like you so they don't post here.

They have been. That was an issue awhile ago, but it's not anymore.

NERF VAYNE, BROKEN AF RIVEN TOO OP RIOT IS STUPID THIS PATCH IS STUPID NERF RIVEN DEVOURER NEEDS A REWORK ALL REWORKS A CRAP HEY I DESTROYED VAYNE RIVEN HAS A 50,001% WINNRATE, NERF DELETE YASOU STUPID META EVER I have an idea to solve a few of kassadins problems KILL KALISTA NERF VAYNE RIVEN IS UNFUN RIVEN IS OK FIZZ IS OP BRAND IS OP PLZ DESTROY OTHER MIDLANER TOO #IHATEMORDEREWORK HOTFIX LEBLANC DON'T BALANCE ZED FUCK THIS MOBILITY

It's hard to find serious balancing issues.

You are clearly just trying to pick on Riot