Hm IANAL so am definitely waaay out over my skis here, but I assume the optics of large employers mutually deciding who is/isn't qualified to work for them lends itself to accusations of collusion and wage suppression.
On the contrary, having a certification not tied to any particular employer (hell, any company could require or prefer X level of that certification) and letting candidates holding that certification skip the grueling, insanely-long hazing ritual they have to go through with every single company they interview at that's in a similar pay-bracket, would tend to do the opposite of wage suppression (versus the current system).
Test once, interview as much as you like for the next, I dunno, two years, no more multi-hour live leetcoding required (the employers shouldn't want to spend money on that, if they just need to make sure you can do it—the certification handles that). Some of the FAANGs already practically publish study guides, so it's not like they're opposed to making the system pretty damn clear and possible to study for. No, it must be that making each interview painful is the point. Else, why would someone who's already passed at two other FAANGs and also the very one they're applying to, a decade ago have to go through it yet again? It's incredibly expensive, and only makes sense if the point is to make sure employees think twice and then thrice about going on the job-hunt again.
We're way past that point. Big Business (i.e. BRT) is currently pushing a new bill that would allow corporations to "buy" undocumented laborers at $2K-$10K for a period of 10 years. IANA-policy-wonk but it looks like it could become law.