I never trust the received file's "track changes", always compare to the latest version I've sent -- and it is extremely common to find a change that wasn't mentioned/discussed, and somehow magically "accepted" or otherwise not tracked in the other side's "track changes". Whenever I point these out, I always got a "oh, yes, forgot about that one", or "I didn't intend to put that in" or "I'm not sure why it didn't appear in the track-changes view" -- but out of tens of these (with multiple lawyers over multiple years), not one was ever in my favor.
Branching might not be as interesting on a single project - but diffing is, very much; and I'm sure it's not more coveted mostly because most lawyers either (a) don't realize how good it makes life for you when you can diff and blame easily, or (b) are abusing the fact that it is so hard to diff/blame on documents, and certainly (c) usually charge by the hour, so some efficiencies are actually going to cost them money if they implement them (a famous Upton Sinclair quote comes to mind).