Getting the underdog on board (AMD) gives them an incentive to do so and get the edge on their largest competitor (Intel). Eventually forcing Intel and everyone else to follow suit if they wish to remain competitive.

A company with 20% market share may be more hungry to make the move in an attempt to propel themselves to the front of the pack (if they're up for the challenge), vs. a company with 80% market share, probably aren't as hungry to change anything if there is no major threat and they are still the market leader.

If AMD were to successfully make the move, it would certainly shake things up.

Assuming any of these assumptions are accurate! ;)