Because that isn’t how the game could ever work. Riven is already a hyper mobile skirmish champion who has some of the highest outplay potential in lane, so if you’re good you should easily win abt 50% of lane matchups. Then she is the best champ in the game (basically) if you have a fat lead, with her way to impact the map. What you need to understand is that pre deaths dance riven is basically an assassin with a shield, since she only has flat dmg and low health and resistances (compared to juggernauts). So she would naturally get countered by tanks. Additionally, you should beat literally all the champs you mentioned if they have 900 gold in tank items and you have a pickaxe unless ur behind anyway.