BCH has gone from around $10 billion market cap to $30 billion market cap in a couple of days. Who the hell has some spare $20 billion to pour into BCH? Buffets net worth is around $77 billion.
Your understanding of the math is flawed. An increase in market cap does not represent a "dollar for dollar" relationship to the amount of money invested in the asset.
Each new dollar invested in an asset has an impact on all the dollars invested before it.
E.g., I invest $10 into an asset worth $1. Then someone invests $1000 when the asset is worth $10. The growth of my shares from being worth $1 to being worth $10 doesn't mean I invested a new $90 into the asset.