The W3C, also known as the people who develop the web standards

Figures. The same people who added DRM to the web standards.

Now, I don’t know what other alternatives could have been used, but I know that URL was among the obvious ones to not use. Something that uniquely identifies you has to be non-transitive and non-revocable by a third party, of which URLs are neither (domain names are revocable, URLs don’t have addressing persistence let alone when you add query strings into the mix, etc). Among the few things that I can think are non-transitive and non-thirdparty-revocable are the good ol’ ssh-keygen keys, easy to generate and all that but I’ve never found a good mechanism or design to query about them.