The 3rd party doctrine is why it is allowed when no law restricts it. It does not prevent Congress to pass a law.

which has been warped all out of any comprehensible reality. It hinges on the idea of 'voluntarily' turning over information. Much of what is now considered information voluntarily turned over isn't even information that people know exist much less that they are turning over much less doing so voluntarily.

It's not voluntary if you don't know about it.