I sense selective memory from Kempin. MS have been trying to sell slates (AKA tablets) for a very long time now and been in the phone biz for some time.
They didn't ignore the tablet, they repeatedly tried and failed to sell them. Gates regularly used to tell anyone that would listen that slates were going to be the next big thing. Admittedly when hardware finally made iPad possible MS didn't move fast enough to dump classic windows on their devices but that's years after he left MS!
Phones, again they had a large share of the smartphone market right up till tech allowed iPhone. And again MS didn't adapt quickly enough. But they were in the market and for a change not really failing.
Social media is more of the same. MS have bought company after company chasing a userbase, they just seem totally incapable of creating their own social platforms. But they certainly acted to get in the game.
To the extent it's even possible to foresee the massive changes, MS didn't sit back and do nothing, they forged ahead but mostly did the wrong things.