Part of it may also be the situation the company is in, and it' mindset, when Keller is hired.
There's no arguing that Keller is a smart guy, but he doesn't design an entire CPU architecture himself. If you're desperate and say "Okay, we are hiring the smartest guy we can find to build our new CPU, and give everything he needs to make it happen", then perhaps you get the AMD64, Zen or the A4 and A5. If you try to just dump a smart guy into a team as just another engineer, maybe you get nothing, like Intel.
Perhaps AMD, who already knew him, just gave Keller everything he need to build a team that can deliver on a new architecture, even when he's no longer there. Same with Apple. Intel on the other hand may have been unwilling to grant Keller the same level of autonomy and control. Then it also makes sense that he would leave Intel, for personal reasons, those being: "I can't work here, they won't let me do my job".
One of the tendencies of shrinking companies is exacerbated executive infighting.
If the company is growing, there are new X-of-Y positions to move up to.
If the company is stable or shrinking, people start watching out for their own careers with knives out.
AMD possibly avoided this because of size & realization of what needed to be done. Intel's too big & old: I would be very surprised if they weren't much more internally resistant to that sort of change.
And one can only deal with your colleagues throwing up brick wall after brick wall on every bit of minutiae for so long, as least if you're talented enough to have other options.
This is an absolutely on-point observation about company dynamics that a large number of people in the tech industry have never had to experience. It's why growth is so critical.
Past a certain size threshold the organizational and social dynamics of human relationships seems to be the predominant factor in getting anything done. i.e. There’s a limit to how big of a headwind we can cope with.
There's no arguing that Keller is a smart guy, but he doesn't design an entire CPU architecture himself. If you're desperate and say "Okay, we are hiring the smartest guy we can find to build our new CPU, and give everything he needs to make it happen", then perhaps you get the AMD64, Zen or the A4 and A5. If you try to just dump a smart guy into a team as just another engineer, maybe you get nothing, like Intel.
Perhaps AMD, who already knew him, just gave Keller everything he need to build a team that can deliver on a new architecture, even when he's no longer there. Same with Apple. Intel on the other hand may have been unwilling to grant Keller the same level of autonomy and control. Then it also makes sense that he would leave Intel, for personal reasons, those being: "I can't work here, they won't let me do my job".