Popularity begets popularity. I evaluated a ClearCase replacement in early 2012 for a large company, and Git is clearly the "nobody ever got fired for buying IBM" SCM.

I looked at hg. It is easier, especially for the windows users. However, git was already coming from a few different directions and hg's simplicity was not enough to tip the scale.

We are now mid-migration. If git devs are listening - this is my biggest nit:

$ apropos git | grep ^git | wc -l 159

I do believe an alternative "porcelain" will eventually supplant the core git commands, making it more user friendly.