Some web sites insist on as much control over our passwords as they can get. They demand that we choose hard-to-remember passwords, they spread the login over several pages, and they refuse to accept password text through autofill or even copy/paste. This is supposed to reassure us, I guess, the way that shoe removal reassures everyone at the airport.
I'm a fan of password managers. No sane person believes that users can memorize hundreds of distinct passwords. A properly secured password manager is essential these days. So I get pretty annoyed when a web site refuses to play nice and let my manager fill in the password.
Fortunately this happens rarely, especially with recent password managers.