This is a bit of historical revisionism. Without the DOJ settlement, I think Microsoft wouldn't have played ball by licensing ActiveSync to Apple (and later, Google).
This single event (2008, I think) drove many people to the iPhone from Blackberry and sealed RIM's fate. iPhone+Exchange wasn't better than Blackberry+BES+(exchange/domino/groupwise), but it sure was cheaper and easier to maintain.
What were they missing?
They also suffered from being too early in the smartphone / tablet market, having to make hardware/software trade-offs that precluded bringing a proper (desktop-like) OS to the mobile devices. Apple as a late entrant could reuse OS X and have developer API's with good forwards compatibility. Microsoft's only option was to ditch the whole OS and start over based on a new architecture, and it took them too long to swallow that bitter pill.
TLDR Embedded systems need tight integration between HW and SW MS doesn't have it because they only do the SW and let others do HW.