If the bigcos had any interest in this, they'd have created such a cert/license. At the very least, they wouldn't make candidates who'd previously passed their interviews, and perhaps those of similar companies, multiple times, do it again.

Since they haven't created a cert, and they do make people re-test, they're clearly doing it for purposes that aren't served by those actions.

For one thing, I don't think they'd be happy about any change that makes it easier to leave. Imagine what'd happen to comp at these companies if you didn't have to do yet another goddamn leetcode gauntlet every time you switched.