If skill was the only thing that mattered then 50+ year old multiple degree black belts would be tapping 30 year old black belts, but that simply is not the case. Marcelo is famous for stating that all of his training is sport specific, but only fought MMA once. There are some people who have evolved, but how come the vast majority of BJJ schools will tell you that BJJ is all you need and commonly downplay the benefits of Strength and Conditioning? A Jon Jones could beat 99% of all BJJ practitioners in a real self defense situation and he is a white belt.
Of the schools I've been to, most of the people are "casuals" - they don't even compete. I was surprised by the number of people I encountered who actually substituted BJJ for traditional S&C. Most of these people just don't like doing it. To be honest, I'm not even sure extra S&C would even make the difference for these people.
Technique deficiencies are often far larger concerns towards grappling success and often lead quicker results. If I drilled nothing but the leg drag for an entire week I would be demonstrably better at the leg drag. Strength gains take much longer to build in comparison. At the higher levels, it matters.
Personally, I've noticed that many BJJ instructors are not small people. My first instructor was 130lbs. Everyone else I've met was 170lbs+. They already have a prerequisite amount of strength/muscle. I'm 160lbs and I feel like if I don't lift my body will not be able to structurally support people's weight.
Finally, its5025 summed it up best - marketing. People don't like to feel vulnerable and they like to feel that their grappling will translate into readiness for some kind of physical altercation. These people also don't like to be punched in the face or risk undue injury, so we start the sport on the ground where someones size and strength can be most neutralized if you have superior position
We had a freak athlete in our class for a few weeks - heavily muscled and extremely athletic. I tried to do the typical X-guard get up sweep but this guy could do the splits past 180 degrees and I couldn't get up. He also pulled my instructor's arm (yes pulled, not "set up") into an armbar and tapped him out. It blew my mind. If you tell a guy like this not to do S&C or to not use strength when rolling, it suspends the illusion that sheer attributes combined with a small amount of technique can overcome a lot of technique.
To be fair though, I have always believed technique to be King. Period. Generally I even believe muscular and cardiovascular fatigue to be a symptom of relatively inferior technique. This is what I tell myself because it makes me feel better and because it's something I can work on. I can work on S&C too and I do. But I have a genetic potential as to how strong I can be. Technique can theoretically be improved infinitely.
You don't see old ass people beating young people. But you do see really good old people teaching younger people how to get technical faster. Nicky Ryan is a prime example. He's getting his man muscles now, but when he first started out he was running thru grown ass man as a prepubescent boy.
