The inevitability of transparency though transaction. Blockchains and wallets.

If we all know coinbase wallet address, as well as other wallets around the world. What stops people from working out individual wallet owners on the blockchain. Tailoring marketing to their transaction history. Learning everything there is about their purchasing preferences?

I'm speaking with friends and asked this question. Need help to answer it?

'I don't want everyone knowing what I buy.' Usually the conversation at this point.