Jump over abilities make sense, Right?

So I like playing champions with jumps and bounces in the case of Gnar, and as I played, I realized that you cannot jump over abilities. For example, I was playing as Gnar against a Rammus and he tried to spin towards me, but i jumped on a minion, intending to use my second hop to get over him, but as I was in the air, I was stunned because i went over Rammus. (BTW I'm basing all of my argument on Gnar because I play him the most and he is the champion I would like to see it on.) I would understand in Rammus was like 50 feet tall, but he is a little Sonic the hedgehog turtle thing that goes "OK" all the time. It would make sense though that I could jump over him, so why is it that I still get stunned in mid air. I can see why with, for example, Lucian's relentless pursuit or Lee Sin's kick because they are close to the ground, but a bounce is in the air. If I can jump over a wall, why can't I jump over champion abilities?