99% of the time it's fine, but if you have even one thing you want to do locally, now you have to use two separate tools.
I'm not sure how many people have an absolute hard requirement for local operation, but it is a nice extra layer of peace of mind.
Git might not be perfect, but it's one of the only tools witch such a large market share. All your projects can use the same VCS, which is really nice.
On the other hand, some programmers seem to really like having different highly specialized tools for every job, rather than adapting jobs to fit the tools, so I'm sure there's demand for a new VCS there.