Agreed, this makes sense in principle.

But what I found, empirically, is that a substantial number of observable SSH public keys are (re)used in way that allows a likely-unintended and unwanted determination of the owner's identities.

This consequence was likely not foreseen when SSH pubkey authentication was first developed 20-30 years ago. Certainly, the use and observability of a massive number of SSH keys on just a single servers (ssh [email protected]) wasn't foreseen.