Financial privacy. You can still report it on your taxes. Maybe some of the coins you now own were stolen and you just happened to get them from the exchange and you are concerned about the fungability of bitcoin in your legal jurisdiction.

You might not want to paint a target on yourself by making known how much cryptocurrency you have, hence you'd like to keep it a secret.

You could say the same thing if you'd live in Sweden and with "normal" money: "Taking out money from the ATM should be automatic red flag, since no one uses fiat except criminals to buy drugs."

You might be running a business and not want to let your competitors know how much you are spending on advertising, R&D, and such like.