What would motivate Warren Buffett to go against the investment strategies and instruments that made him filthy rich? He has built his whole empire on the old traditional Fiat based systems and he is too old to make a major change now.
Keeping his capital as safest as possible is the most priority of Buffet, not invest and earn more money.
Bitcoin is also a high risk investment and mostly unregulated, so they will be going up against the people that are supporting them with this "insider" knowledge, like the government.
(The same government that bails them out, when they do make mistakes)
Investing in strange asset or in companies or industries that Buffet does not have knowledge of and experience on is never his priority. Bitcoin is extremely volatile, that violates Buffet's rules. Blockchain industry is very strange for him, that violates his rules again.