Why hasn't Riot ever touch the riven

Since her implementation into the game there has been a Non-Stop complaint about Riven. She has a stun every second on her house and one on her other ability all while being mana free. Yes this is stuff we already know but this is also very problematic how many champs in the game can really do with a stun every few seconds?

Once she starts bouncing around you just let her do her thing there's no real way of stopping her and even if you try she dumps you. This is a huge anti fun gameplay mechanic that they haven't looked at for years. Why do they insist on giving Lux 3-5 skins a year but refused to tweak this champion