I thought this a few years ago when I was more junior as well. In open source circles git has been used for quite awhile but my company just recently moved one of our repos from TFVC to git. A Fortune 500 company I worked for was still using TFVC for some legacy products. Another product from a acquisition used Subversion and the migration to git (even with the company using GitHub Enterprise) still took almost three years.

Getting the inertia amongst developers to migrate to a different SCM can be quite the challenge.

Edit: initially said migrating to git was a challenge. But really it’s migrating from any SCM to another that’s challenging.