I don't know the true rationale, but if I remember correctly a Chrome dev provided some really dubious reasoning one the related issue tracker item, something l

I don't know the true rationale, but if I remember correctly a Chrome dev provided some really dubious reasoning one the related issue tracker item, something like "someone could MITM the connection and change the basic auth message to 'please enter your YouTube credentials'". Well guess what, if I MITM your connection, I can provide a much more convincing HTML representation of the YouTube login page! I guess the grain of truth that was in there is that this is one of the few times where a server-provided string is presented as part of the browser's UI, but I am sure there are better ways to highlight that the browser is just quoting the server than outright not showing the message. Edit: It seems like a dubious security report was the origin of this, not a developer: https://bugs.chromium.org/p/chromium/issues/detail?id=544244 https://bugs.chromium.org/p/chromium/issues/detail?id=544244