When you take the advice of Warren Buffet, it is something excellent, but if we go to the stock market you must wait at least 8 or 10 years to see results of the investment, on the other hand, in BTC you see results after 3 or 4 years, and the most likely is to see a great profit, that is what many do not see.
To be fair I think Bitcoin expected timelength to make the same profits as stocks is also getting longer and longer. 2014 to 2017 20x was three years and now 2017 to 2021 a longer period of 4 years, it is "only" 3x.
I guess we know why Buffett is starting to like Bitcoin (by not saying so much against it anymore).