Yes, likely that too. But on the other hand, the lower level league players, low Bs, Cs, tend to be less educated / less smarter (yes the two may not be the same, but you can tell when someone is dense or not LOL). The less educated may play as much as the more educated but they don't get to that same level of knowledge and/or skill and it will likely take them longer to reach that same level.
I think there is a innate curiosity in those that go after more education and are smarter, which causes them to grab all the information and technique that they can from anything, not just pool. And if those players get into pool, they can get to a decent level, only stopped by their ability to line up the shot properly due to eyes, whatever, and how long they can spend playing.
I would have to agree with all of this... except for the use of "less smarter."

People of higher intellect can grasp ideas, strategies and concepts more easily. This is a huge advantage in billiards, and it can allow a highly intelligent person to get to a higher level more quickly than someone who has a harder time with learning those things.
You then get to a point where knowledge isn't so much the problem, and executing those strategies and concepts becomes the key. When it comes to execution, repetition is your teacher. Someone who is mentally gifted will be less likely to put in the table time needed to hone their execution simply because they have so many other options. If you are able to do many things at an above-average level, it's hard to concentrate on just one of them... especially if the other things bring you joy, as well.