It's obviously not as simple as you conjecture. For the simple reason that the blockchain is simply a record of transactions on anonymous public keys. Generating a new private-public key pair can be done trivially and secretly.

Everyday thousands of illicit transactions are carried out on the blockchain. The US government has never shown a shortage of force when it comes to stopping drug dealers. Yet the number of people who've been arrested based on blockchain analysis can be counted on one hand.

See Monero. Transaction senders, recipients, and amounts are hidden by default.