Everyone who owns shares in a retirement fund benefits from the privacy afforded by these instruments. If every beneficial owner of every corporation had to be publicly registered, that'd be an enormous proportion of the regular public!
Think about what it would mean that anyone could, at any time, look up all the investing choices of anyone in the country.
It would be truly fascinating information but yes in our current level of innovation and maturity, totally bonkers.
It's totally a thing to have trades pegged to US politicians' investment choices, because they often have the knowledge not available to the public to make "better" (financially) decisions.
As per your first comment, this is generally the difference between an active and passive investor which usually works out to someone who owns about 10% of any given company. It's probably a little too high as it isn't hard to imagine a cabal of 11 wealthy tax dodgers playing games with the reporting requirements.
I believe most laws getting enacted which are addressing corporate secrecy are primarily targetting the active owners of companies and usually unnamed beneficiaries who have a benefit to the company/trust who aren't specifically owners, who can reap the benefits of the company's assets without strictly their name of the deed so to speak.
Again, most of this revolves around what is asked by government officials for auditing and less about what information is being dumped into public information.
Think about what it would mean that anyone could, at any time, look up all the investing choices of anyone in the country.