The same reason why GNU Taler is anonymous https://taler.net/

The EU can still suck taxes from the transactions of Taler but at least they have no idea what you bought. Why should the payment middleman have a complete itemized dossier of your personal purchasing history just you and the merchant should share the details of the purchase beyond the total amount paid.

> Why should.... merchant [] share the details of the purchase beyond the total amount paid

Because the government has a legitimate interest in taxing different goods at different rates.

They have an interest. Whether that interest is legitimate is at the very least debatable, and not beyond questioning.

Do you agree that taxation is a legitimate lever with which to effect economic and social policy? Vice taxes, for example, are much saner than outright bans for everyone involves, and tax incentives can drive the adoption of things like solar panels.

"If you've nothing to hide you've nothing to fear."