The open-source, "time tested," self-hosted solutions do not check that the website you're trying to paste a password onto is the website you should be pasting the password onto. That is a real and serious security risk, and the fact that the open-source solutions don't attempt to solve it does not mean it should not be solved.

I think a lot of people feel uncomfortable giving a proprietary product access to their passwords, and feel more comfortable doing the copy-and-paste themselves. But compromising security for better comfort is not a very good strategy.