Unless, these criminals are also long-term bullish on bitcoin hence why they prefer holding it. 

Kidding aside, bitcoin is traceable and all, until they learn how to coinjoin/mix their coins well(and not mess up their tracks), then that'd be a problem. Also taking note that developers are trying to come up with ways in making bitcoin more private.

Also, correct me if I'm wrong, but unless you're a mid-high class criminal, I don't think anyone is even going to trace your transactions.