Why? Because the full domain would be shown instead of the full URL. This is exactly the sort of thing the URL address bar can prevent with this. Vivaldi can then advertise as a feature the new anti phishing address bar.
You can close this topic unless someone else is interested in it. I installed Windows 7 again because I was fed up with this and other issues/bugs in Windows 10. On Windows 7 Vivaldi/Chromium is working fine as it should be.