The reason is that people who want to succeed in investing are looking for someone who has already succeeded, in order to repeat his success, they are looking for the best in investing. Since Buffett is the best in investing, so many learn from him investing. Perhaps Buffett could succeed in investing in cryptocurrency if he knew this, but we dont know because he doesnt understand it.
He surely does understand it and they way it works, probably more than most of the members here do and that's because he has a ton of experience from investing in all kind of projects. I think the problem that he has with bitcoin is that it is a very risky investment and most of those big investors usually don't want to take those kind of risks because it's unnecessary since they could make the same profits from a different business while the risks are much lower.