Actually, very often they don't... Porsche shares, if you wish, are the representation of the public perception of value of their cars, service network, brand, cash in the bank, etc. They are the quantifiable proxy of those values. Cryptocurrencies do not proxy anything. So, the only way to measure their value is by "what people are willing to pay". And that doesn't have to be bad, a-priroi. Its just different thing. So, the cap of crypto _is_ nr of coins time price per coin, where ppc changes heavilly over time. So the "market cap" of crypto is not constant - it changes very rapidly over time. <crypto_name_here> could have a cap in billions today and zero next Thursday. Hence, there isn't much sense in trying to define/measure it.

> I'm pretty sure that currencies have a value in a deeper sense then just "What people pay for it".

You should share your ideas.

Not really.

If you were able to buy 100% of Porsche, you would be able to sell it again for a similar amount because the business would continue to operate and make money. The value is in the constant stream of customers that give Porsche money in exchange for cars.

If you bought 100% of Bitcoin, you would not be able to sell it for much because the value is in the widespread ownership of Bitcoin and its use/potential use as currency. Just like the 'market cap' (money supply) of USD is a few trillion but only so long as a few hundred million people hold USD.