Bitcoin is actively used as a payment method for drugs, weapons and other illegal activities. When buying dirty bitcoins, you are an accomplice.
FATF recommendations, as well as AMLD5, which entered into force on January 10, 2020, oblige all exchanges to check the sources of cryptocurrency origin and block suspicious funds.
There are thousands of posts about exchanges blocking suspicious bitcoins. Do checks each time you trade and this will cut the risk of bitcoins block and loss.