Asking a world that is used to what came out of Xerox PARC to switch back to 1970's technology on teletype emulators is...the only word I can think of is Quixotic.
To write software, I can use a CLI text editor, a basic GUI text editor, an advanced text editor like Sublime or Atom or VS Code, or a full on IDE like the JetBrains products. I have so much choice, and all of these are interoperable with each other and have different places where they shine. All work with git. I just don't think the same thing can be said for the document-creation workflows around law and such.
That's my general response to "why use 1970s tech?", though I guess I'm being a bit unfair here. Word is, in some ways, a marvelous piece of engineering. The whole Office suite is. Unfortunately, thanks to path dependence and business strategies, it's also locked in a place where it's not interoperable with anything outside the Office ecosystem by default.
I guess I have an answer to the age-old question: in sci-fi shows, how come nobody in-universe notices their computing technology is, in many areas, ridiculously inefficient and ineffective compared to the old XX/early-XXI-century tech? The answer may be, the sci-fi future tech is built on so many layers of lowest-common-denominator, walled garden, non-interoperable tech that people no longer know how interoperability or efficient computing looks like.
“Being old” is probably the lamest way to claim something shouldn’t be used.
Having to use MS Word in the cloud doesn't really scratch the itch I'm talking about either.
That's cool about Office 2019, I did indeed not know about that. Can I perform these Sharepoint-enabled changes while offline? It seems like all of the things you are talking about require a centralized online server in order to do. Regardless, I do not think there is a conflict between the statements "you need Sharepoint to do these things" and "Track Changes cannot do these things".