Because the amount of skill involved isn't the issue, the issue is the agency you have against it.
You can dodge Lux's Q, R, and now her E. You can stay out of Annie's range while her passive is ready. Cho'gath...Okay. Cho'gath is bullshit. Malzahar, you can dodge his Q, you can avoid his E passover, and you can kill his voidlings. His R is point and click, but it doesn't enable him to land any part of his kit, unless it was already going to hit.
Zed? If he ults you, you either have enough effective health to survive him, you have Zhonya's, or you're dead, assuming he's good. He can take all the skill in the world. He might have to hit you with all three E's and Q's from him and his shadows. But once he ults, it's 100% on him to fuck it up. It's not a "Oh, he played that better than I did, oh well", it's a "Oh, he had enough skill, so I died". The difference is that you get no skill expression in avoiding him. No matter how perfectly you time flash, he's landing his E, and he's very likely to land his Q. And odds are, he's getting an auto in. And you're losing most - if not all - of your health.
Yasuo? He has things you can dodge, and stay away from, sure, and he takes a good amount of skill, but if you can't outrun him, he's going to Q>Q>EQ>R you.
Talon? Don't even joke about him being high skill. He's pathetically low-skilled. And the only thing you can even try to dodge on him is his W, and that's basically never going to miss on the way out.
tl;dr: The problem isn't that assassins are low skill. The problem is that our skill doesn't matter against them, only their skill matters, and that feels like bullshit to play against.