[forty]

"people" don't know what is Emacs, vim, tr or urandom for any reasonable definition of "people".

I work for a company that makes a password manager, and at least one clear benefit, versus copy/pasting from somewhere, even for tech savvy users is phishing resistance (the password manager browser extension should not fill your password on a website which doesn't match the website associated with that credential) which is how password gets stolen in practice when they are not reused (not re-using is the main benefit of a PM, but your home-made system does solve that issue too)

They are other benefits more on the convenience side (mobile as you mentioned and even not having to switch app each time you need to grab a password...) which matters more for most people than security (or so they believe at least)