Many people don't understand cryptocurrencies, and if criminals want to use them, they need to know more about them to use them, so it's easier to use fiat currencies than bitcoin or other cryptocurrencies.

Borrowing money to invest is very risky. The price of Bitcoin is volatile and difficult to predict. When market prices change, it is easy to be affected by market sentiment and make wrong decisions that lead to losses.
Without familiarity with crypto knowledge and trading strategies, it is difficult to guarantee a consistent profit in the crypto market.