Office for the Mac was hamstrung in a way that made it usable for home users, but difficult for businesses. There was no Outlook, no Visual Basic, and IIRC: No pivot tables in Excel, no OOXML until 2011 (4 years after Office for Windows), less integration with Microsoft's backend servers (Sharepoint, etc.), and some other missing features. I'm also thinking that Group Policy management didn't work or not as well.
Much of that was later fixed, but for a long time it was another powerful reason for businesses to use Windows.