There is also mental friction with learning an entirely new tool. `jj` is different enough from `git` that one can't transfer knowledge. Currently the documentation is not good enough to assuage that issue.
>>dlisbo+(OP)
Frankly, this is a rather poor, uninformed excuse. Most people who try it grok the concepts in days. And they feel right at home in weeks. That's when you start hearing, "I'll never go back."