Why do cryptocurrencies have value?

Answer: Because people agree they are scarce and will trade for them

Because the cost of mining keeps their price from falling — Wrong. Mining costs can affect how much new supply appears and can matter to miners, so the cost side is not irrelevant. But mining costs do not set a fixed floor under the price: if buyers stop wanting the coin, its market value can fall below the cost of mining. Price comes from what people are willing to pay, not from production expense alone.

Because people agree they are scarce and will trade for them ✓ — Correct! A cryptocurrency has value when people accept it as scarce and are willing to trade goods or services for it. Its supply rules can limit how many coins exist, while shared trust and network use make holding it worthwhile. That value is not guaranteed by technology alone; it depends on continued acceptance.

Because they are expected to replace all money soon — Wrong. Future adoption could change demand, and that possibility can influence what some people pay today. But the current value of a cryptocurrency does not depend on it soon replacing all money. It reflects present scarcity, usefulness for transactions, speculation, and trust in the system, while replacement of existing money remains uncertain.