I really really want this to be true. Unfortunately I can just see some ambitious PM picking this up again and trying to push it even harder. "The real reason the previous initiative failed to gain traction was insufficient market education."
By understanding the circumstances and work of the people you're managing, so that you can subtract confounding factors and separate their influence from everything else. There is absolutely no substitute for that, but because it takes actual work and attention, businesses the world over have been trying to replace it with paper thin metrics since time immemorial.
I'm pretty sure that's the primary reason, which won't change anytime soon.
I'd also expect many publishers that adopted AMP to jump ship now, which means it will slowly die away.