Telling people they have Stockholm syndrome is not a good way to convince them to change their behavior.

Yeah that's probably not the best way to express it. Perhaps it is more like:

Git is huge and complex to learn, and some people have spent a lot of time to learn it - hundreds of hours.

Now, eyeing jujutsu, they expect that for doing this complex task with jujutsu they will again have to learn a very complex interface, with a lot of effort, and they decide it probably ain't worth it. Which by the way, for software is a reasonable heuristic most of the time.

So if somebody tells them that jujutsu is less effort to learn to do complex tasks, they don't believe it and that's it.

It also seems to happen frequently that people try jujutsu, but it does not click for them, they try commands but they do not get what's the advantage - perhaps because it is too different from git. And later they try again and it clicks. Steve Klabnik described that for himself.

Moreover some people don't need to do complex tasks.

And people in general hate it when interfaces change in unwanted ways. Which is human nature too and a valid way to allocate time and attention, which both are a scarce resource.