it's not because Riot hates MF, there is an inherent truth about off builds ratios, they are there because in the past there were items that gave a bit of AP, so when you built those, you wouldn't feel like it's a waste of gold because you're getting an item that has AP... for example, you got to scale with Triforce no matter what because sheen used to be made with an amp tome
This is what riot calls extra power, when they find an OP champion, Riot tries to keep what made the champion interesting in the first place, for example, for MF is her lethality build mostly because it has a crazy damage output, so they try to keep the crazy damage while removing power in areas where it's not needed and often times extra ratios are the perfect target for this
You might say that MF doesn't build ANYTHING with AP and I agree with you, she doesn't but you'd be forgetting that there's a great amount of AP distributed throughout the game, with Baron and Supports buying Zeke's and whatnot, lowering her AP ratios would cut down these edge cases enough for her to have less free power from outside sources and ultimately making her easier to deal with