You have to remember that grappling skill grows logarithmically. This is actually true in every martial art as well.
Think about what you were like when you were a complete beginner. Someone with 1 year of experience could basically submit you with whatever they wanted in about 30 seconds. You were completely dominated and had no idea what was happening. The only thing you realized was that you were being choked and locked in extremely painful ways.
Now that you have 1 year of experience, who can make you feel this way again? Usually only people with 10+ years of experience. Only they have enough skill to completely dominate you with whatever they want at will in a way that is beyond your comprehension.
Although it is kind of depressing, you will never, ever improve as much as you do in your first year of grappling. In your first year of grappling, you go from someone who got beat on all the time to someone who can beat on a lot of other people. In your second year, you will not improve nearly as much. It takes many more years before you notice the same level of improvement again.
Skill levels tend to even out a lot after the first few years of experience. Imagine your instructor started training five years before you. When you first start, he will crush you completely. But when you have 20 years of experience and he has 25, do you still think he will win? Maybe, but not by much if he even can.
So I think you are noticing this discrepancy because you are expecting more experienced people to improve at the same rate as you. This never happens because after about a year, you tend to know all of the basics of grappling. The advanced details do make a difference, but not nearly as much difference as the basics. That's why it takes so long to get really good.
