What you're up against is resistance to change and reluctance to take any kind of risk.
We are terrified of change, at least in this regard. But in other arenas too. Most people want an easy life, and that means sticking to suppliers you know and have existing relationships with.
Also, most don't want to rock the boat. Don't want to say, "Hang on, what we're doing might have worked years ago, but is it still the best option?" Nope, most just keep their heads down and do what they're always done. It's easy, predicable, and nobody will lose their jobs for doing what they've always done.
Conversely, if you are the driver of change and it doesn't work out 100% as management expected, or there's a hiccup, it's your ass on the line.
So people stick to what they know. What's been proven.
It literally doesn't matter if AMD delivers 5x the perf at 1/2 the cost. They represent change for many. They represent risk.
And it's really hard to overstate the aversion that most places have to risk and change. They hate it.