Which, even though you know it is not the case, market size is taken to mean that $Billion has been invested in Bitcoin, or $Trillion, etc... That is not how money works.
True. The same is also true for valuations of companies, some tech companies are now worth more than the GDP of small countries. But that doesn't mean they could ever be sold for that much - as soon as you start selling the price goes down on the rest of the shares.
"Market cap" is just a mental shortcut, a hypothetical estimate used to compare investments.