Who knows? Too big so different people pull in different directions?
But you see it very clearly in Outlook, they have had several different versions of Outlook. Another example is OneNote - They had a real good desktop product, then they developed a different version for “some online environment” - it became their default, and was badly inferior, and then they announced that they would discontinue the desktop version. After a year or more of protest, they relented. But by that time I had tried various other topics, and finally settled on Coda. In the process they tried to trick you into moving into OneDrive as a storage environment. Between OneNotes and two storage systems, I lost a LOT of information…
Had a similar experience with SharePoint, built a nice document repository, managing statuses using tags (Completed in English, Ready for Russian, All completed, etc). Was really impressed with the tool. Then I upgraded Windows, and they not only installed edge, but disabled IE. And Edge could not access SharePoint, only through File explorer if I remember correctly … So I had an anxioius time for a while, until I found I could re-install Internet Explorer.
You had the same with Office desktop, Microsoft 365 an now lately Office 365. All work slightly different.