People have added better UIs on top of git. The problem is they don't come installed by default out of the box, and unless everyone else you work with is using them too it becomes quite hard for you to communicate properly over git issues (especially in writing development workflow docs). hg has a better UI out of the box, and is notably easier for new users to pick up and become productive with.

You're underestimating how much inertia is created simply by being the out-of-the-box default, and how hard that inertia is to overcome even by better alternatives.