[lucideer]

I'd guess it's a perfect-storm combination.

As the above commenter mentioned: a combination of hardware & software gives Apple and inherent advantage, which—along with Apple just having a culture of prioritising UX in their products (and MS kind of being in decline at the time, before their recent resurgence)—would explain the pre-iPhone trackpads being ahead of their competitors.

With Surface, while MS do control both elements, they're playing catchup on years and years of progress by Apple.

Combine all that with the recent mainlining of iPhone R&D and catching them seems really really tough.