OK I thought of a better reason for Microsoft to keep Xobni independent. This way a business has to pay for both Outlook and Xobni!
If Xobni was rolled into Outlook, then Microsoft could only charge for Outlook (possibly force an upgrade to a new version). If Xobni was an independent (though Microsoft controlled) entity, every enterprise Xobni user would willingly pay for Xobni and have to still pay for Outlook. Further depending on the utility of Xobni to users, they could charge more than Outlook itself! So maybe Microsoft sees the potential to double its enterprise email revenue and is being patient.
If Xobni was rolled into Outlook, then Microsoft could only charge for Outlook (possibly force an upgrade to a new version). If Xobni was an independent (though Microsoft controlled) entity, every enterprise Xobni user would willingly pay for Xobni and have to still pay for Outlook. Further depending on the utility of Xobni to users, they could charge more than Outlook itself! So maybe Microsoft sees the potential to double its enterprise email revenue and is being patient.