Basically Buffet and others old blood investors are not believing if non-regulated currency. For them current state of Bitcoin is similar to Wild West.
They don't believe government and politicians will leave bitcoin unregulated for long and bitcoin must change to be on par with other payment methods,
when that happen bitcoin will lose its worth, so it is better to leave it alone - Buffet's logic.
They will never get it, they are simply from the old generation, it's the same as trying to explain Bitcoin to your parents, they will never get their heads around it, it's just too complicated for anyone that hasn't been born in the era of internet OR if they are engineers or somehow computer related even if they are older.