At some point you have to decide whether the the perfect (everyone using Windows phones/tablets and MS Software) is the enemy of the good (a lot of people using MS Software).

Microsoft has for whatever reason never hit the target with mobile platforms. I guess the Windows Phone is decent enough by some accounts but was just way too late to the party.

So they can try to make money selling mobile software for a mobile platform that nobody uses, or they can just accept reality and sell the software on all platforms.