To echo what you were saying, binary distribution on Linux is indeed tough.
A while ago I needed to experiment with an old file format, and I found a Linux binary of a proprietary tool from the 90s. It linked to libc version 5 (from before the Linux world adopted glibc). It would have been complicated to get it running.
I found a Windows binary of the same tool. Put it on a Win10 VM I had for other purposes. No issues.
Stable binary ABI of userland is something the Linux world doesn't do well. Win32 and COM are really good at this.
If that tool linked libc statically, it would have worked. Linux does provide a very stable binary ABI in form of syscalls, so long as you bundle all your dependencies. The problem is that nobody does it that way in practice, at least not with the commonly used tools.
This is the real elephant in the room. Despite all their other flaws Microsoft has an excellent record of maintaining their software well after release. Particularly when it comes to their core products like Office or Windows. WIN32 programs or XLS files from 30 years ago still work on the latest versions.
If Microsoft didn't have this commitment, then porting Office to Linux as an experiment might be worth it. Even if there's a 10% chance it takes root, that's good revenue. But even if only a small base of users bought Office Linux it, Microsoft's reputation would require them keep maintaining it for decades.