It's the first of many iterative design changes coming to Github. It'll all make sense soon enough.
Why not release them when they make sense as a whole?
Agile!
Maybe they follow the "make it worse, then make it better" approach to user experience.
Even if the end design is objectively worse than the previous/current one, it will feel better compared to the intermediate versions. That might make the users actually complain less in the end.