One issue with this is that URLs for sites can, and in my experience, often do, change, while logins remain the same. A password that uses the URL/site itself m

One issue with this is that URLs for sites can, and in my experience, often do, change, while logins remain the same. A password that uses the URL/site itself may no longer work unless you can remember the old site. That's a headache. I used to have my own mental model of generating a password based on a URL, and it eventually failed several times over because of this issue.