Most people who bought $BTC at the price of $64k are making a profit but

If 5% of them sell, the rest will no longer be "profitable"...

This is a useful measure for things with higher trading volume than that capitalization and/or stable demand regardless of trading volume. For example, Jeff Bezos could sell all his shares in Amazon and someone will buy it, guaranteed. The same goes for almost any decent-sized company's stock.

Gold is at a midpoint, where demand is not actually infinite (despite what some gold enthusiasts say) but there is still enough that a moderate amount of gold being sold onto the market will cause prices to plummet. .

The problem with cryptocurrencies is that even Bitcoin and Etherium behave like thinly traded penny stocks, where a relatively small change in the level of activity has a large impact on price and for the most part " market capitalization" is not active in the market.

For example, Germany sold about 50 thousand Bitcoins to the market, and as a result the price dropped by more than 10%, and it's not like they sold it all in one place or all in one day. Compared to the total number of tokens, that number is about 0.25%, and it has caused a decrease of more than 10%...

Well, in terms of cryptocurrencies, I don't think Market Cap is a useful statistic, given how volatile the markets are and how sensitive they are to what is considered selling pressure small in any other market.