i dont think anyone thinks it's worth that on its own, but you need some kind of user management (entra id in this case), some kind of cloud storage (sharepoint in this case) and some kind of standard document format (docx, xlsx, pptx in this case) in any company.

of course you can do all that with open source stuff but office is just easy to buy and hard to get rid of once you have bought in. the bigger your company the harder it is to migrate.