what does this matter anymore with office 365?
You can't use the web version offline, they are not a PWA, for instance.
Don’t get me started on Excel.
Business and engineering software uses Windows APIs to integrate with MS Office and Active Directory. The APIs are not portable and hard to replicate on emulation layers. The software is old so expect a huge pile of examples of Hyrum's law. So you need bug-for-bug API layer implementation to run those software elsewhere.
Migrating companies off from that software is actually harder than creating a clone of Windows.