> What’s your motivation for doing this?

Maybe he, like me, just thinks there is no reason for history, form data, cookies and all that stuff to be saved after starting a new browser instance, except in rare circumstances.

> What would the benefit be of storing them in a third-party password manager

Decoupling, less dependance on a specific browser. "Unix philosphy".

A concrete example of why a 3rd party pw manager is useful- git(hub/lab) credentials. On both sites, I can easily want to enter account credentials in a terminal as well as the browser. Not every password will exclusively be used in the browser, and 3rd party managers are handier outside the browser.

To make the browser stateless and, thus, harder to track.

Do you use any form of tracking protection (either as a built-in browser feature or via browser extensions)?