There were simple, streamlined solutions for this a decade ago. Nobody used them and many of them died. Some still exist out there like zombies. I was shocked to see inames.net is still out there.
The example I usually bring up is Windows CardSpaces, which shipped with Windows as recently as Windows 7. It was easy for people to get conceptually. It was easy for site admins to implement. But it never went anywhere.
When I talked to people about identity solutions like this, there were problems on both ends. From the user side, an identity solution needed to solve an obvious problem and/or be easier than the status quo. For many users, the status quo is to give out personal information freely and use the same username/password everywhere. Anything that adds choices or variety to the process is too much friction for little perceived benefit. Even if the actual process is simpler (clicking a card) than the status quo (filling out a form), there's a mental cost in adapting to something new.
For site owners, there was the added difficulty of educating and supporting users about the new identity solutions. But, the real biggie was that they'd lose the ability to collect & sell all that personal data. That can be more profitable than advertising, and it's a revenue stream some sites can't live without.
