Market cap defined as price * total supply is a fallacy because it does not account for liquidity. Order books are fairly [0] thin even at the larger exchanges that you only need to buy/sell a few thousand BTCs to have a significant impact on price. If you consider the potential of wash trades it gets even easier. Bear in mind that up to 1/3 of all bitcoins mined could have been lost[1] and only a small amount of actively traded anyway.
A good parallel would be that Tesla is valued by the market at 500+ billion, but it's impossible for all shareholders to sell their shares for 500 billion because there are no buyers with 500 billion in cash waiting to buy Tesla stocks, and if anyone tried the price will crash after the first few percent has been dumped.
A good parallel would be that Tesla is valued by the market at 500+ billion, but it's impossible for all shareholders to sell their shares for 500 billion because there are no buyers with 500 billion in cash waiting to buy Tesla stocks, and if anyone tried the price will crash after the first few percent has been dumped.
[0]:https://www.bitfinex.com/order_book [1]:http://fortune.com/2017/11/25/lost-bitcoins/