Well, MS needs to go to mobile, it absolutely yearns it. It has no choise.
The desktop&server business is profitable but there's no growth up there. The only business in town is the mobile business, they've realised it and haven't got it.

Now, they might well be throwing money to the fire but oh boy they have got plenty of that stuff. If there's a remonte chance that this aquisition is going to turn profit one day they are risking all to do it.

And just as I said, shareholders are just Bill & his bedboys, the rest don't have a say on it.