No COM integration, no VBA and no Active Directory support. Business and engineering software uses Windows APIs to integrate with MS Office and Active Director

No COM integration, no VBA and no Active Directory support. 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.