First thing is to do runs of a game you're interested in speedrunning without worrying so much on glitches. Over time, you learn things of the game that helps you understand how the glitches work...or sometimes you find out that glitches are just not for you. There are those who love watching glitch runs, but there are also those who really enjoy glitchless. Runs that really focus on beating the game quick without abusing much of the programming. Just keep trying glitchless and eventually you'll get it.
I'm not as insane as some of the posters above, like SDA and his 29 hour run, but I just run Legend of Mana. The shortest category is Dragon% and each route takes more time. Then you have All Routes which are about close to 3 hours and 100% which is close to 7 hours.
I'm sure people have stated it above, but it ultimately comes down to the fact of balancing. When i see Expert, I see someone that one would have a great amount of time and knowledge with a game to the point that they know how all the skips or steps in a specific speedrun. So if such a thing existed, it would be that you would have reset your name off a leaderboard if you move up or down the difficulty. In the end though, people would end up stating with Beginner just to stay high on the leaderboards. Not many people would specifically go out of their way to learn the route for the Expert leaderboards.
Probably help to pay attention to the site, would have seen the forums! XD I'm Quatropus, nice to meet everyone! Last year I was racing Binding of Isaac under a different name, but decided to move on because I wanted something different. Watched SGDQ a lot this year and was super interested in learning. I've currently been running Abzu, Inside, Ori and the Blind Forest, and now I'm currently working on Legend of Mana. Again, nice to meet everyone! :D