Probably because Luke isn't a programmer and many of the people he works with would get confused by actual version control.
This is Luke, he should teach them version control. Perhaps a simple system like svn would be better than git (but it requires a dedicated server...)
The simple functionality alone - diff/merge tools, merge tracking, logs, tagging/branching, retrieving old revisions - is very empowering for any text-based collaboration. Programmers invented it, but that's no reason nonprogrammers shouldn't use it.
I haven't used dropbox beyond a brief trial a year ago, but I seem to remember it has a primitive version tracking system built in. If it does, it's sure to be much worse than e.g. svn with a good gui like Tortoise. (Those who do not understand, are condemned to reinvent a poor copy...) People who use that, especially, should switch to a real VCS.
Git GUIs are considered harmful, but... they really make sense to non-programmers. This is probably the best way to introduce non-programmers; they can understand an app that does version control, but asking them to understand the terminal environment AND command line git might be too much.
I have often benefited from recommendations for Things I Didn't Know I Wanted.
Given that Less Wrong is a community of unusually intelligent, critical, and self-improvement-focused people, I suspect we can generate a pretty helpful thread of product recommendations — perhaps even a monthly thread of product recommendations.
Rules: