When you're #1, you can go all-in on your own proprietary stack, knowing that network effects will drive your market share higher and higher for you for free.
When you're #2, you need to follow de-facto standards and work on creating and following truly open ones, and try to compete on actual value, rather than rent-seeking. AMD of all companies should know this.
1) billions of dollar at the stake
2) one of the most successful leadership
3) during hottest peroid of their business where they heard about Nvidia's moat probably thousands of times during last 18 months...
and you call some decision "crazy", then you probably do not have the same informations that they do
or they underperformed, who knows, but I bet on #1 reason.