It's how the banking system and the financial markets authority work in Europe. With the European laws, you're not so free financially speaking. you can't make whatever you want with your money.
To give you an example, in my country, your account is flagged once you hit 5000€ worth of transactions within 30 days. So, the bank has to abide by the law and report your account to the authority govt. then the authority will scrutinize the last transaction to see what you're doing with your money.
Dirty coins or not doesn't matter since you don't transfer coins to your bank account, but you trade for fiat and only then transfer outside.
An exchange or a web wallet can also ask you from where the coins come from and what is your activity