Well yeah, that too. But I was doing that manually before anyways, didn't really change when I started using a password manager, except the passwords of course

Well yeah, that too. But I was doing that manually before anyways, didn't really change when I started using a password manager, except the passwords of course got a lot stronger since there is no need to remember anything. But the domain binding just isn't possible without technical means, hence I see that as my own top reason, I suppose :)