Microsoft has struggled with its strategy to port its apps for iOS, acting sometimes reluctantly and timidly in the eyes of some critics. iOS and the Apple devices it powers have crushed Microsoft's Windows Phone OS smartphones and Windows tablets.
Thus, some believe Microsoft has refrained from porting its products to the Apple mobile platform because it doesn't want to add to its appeal. In particular, the company has been criticized for not having a full-featured, native version of Office for iPads, but Microsoft officials have acknowledged they're working on it.
However, Microsoft has ported some of its products to iOS, including the above-mentioned SkyDrive as well as OneNote, Lync and SharePoint.