That's because Intel was on the single-threaded performance bandwagon for at least one beat too long. (Which was at the time of AMD's first renaissance with Opteron and multi-core.) Which a certain Intel exec--I was an analyst at the time--told me was because Microsoft had such a lack of confidence in their ability to pivot to multi-core architectures. And I have no reason to especially disbelieve that.

Interestingly, the shift to multi-core on the desktop hasn't been the big problem that a lot of people feared it would be. I remember hobbling on crutches cross-country to SF for an Intel quad core (?) launch and there was a lot of hand-wringing on the topic but mostly things worked out.