The way PES games are coded, changing one thing might break the entire game.
Don't take my word for it, look at what Nesa and Juce have done with the Gameplay Module. Think of it as sliders. You change one decimal the wrong way and players get looped in animations or the world stops turning.
I know, you're probably going to say that it's because this is just a change in the game's behaviour, and Konami could fix that. And you're probably right, but what I'm trying to say is that for Konami to add sliders, they may need to start from scratch.
I'm not a game programmer, but I'm a Web Designer. And it has happened many times to me, when I was starting to build my first websites, than when you start off with the wrong foot and you don't even realize it sometimes you have to start all over again to fix 5 little mistakes you've been carrying over throughout the whole coding. So you have to recreate the same website all over, from 0, just keeping the code clean this time. I think PES is just like that. The've been dragging around some trash-programming from PES 2014 and now it's getting harder and harder to get rid of, unless they start fresh.