Becaude you can't observe directly how much every person really values the assert, only the market-clearing price. No serious economist/trader thinks that 5% of

Becaude you can't observe directly how much every person really values the assert, only the market-clearing price. No serious economist/trader thinks that 5% of the supply can be bought or sold for 5% of the market cap. This is exactly the same whether the assets are commodities, cryptocurrency or equity yet we still talk about market cap as a useful proxy.