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.
There are a lot of advantages to using git, in part because it was developed for a massive project (the Linux kernel) so it's very thoroughly tested, in part because it's exploded in popularity so a lot of a tools, integrations, and documentation are available for it. However, it's not the alpha and omega of version control. Some people prefer the interface of Mercurial, some people use Fossil because it integrates issues and wikis, others have stuck to older tools like Subversion, and still others are experimenting with new approaches like Pijul.
Source Depot is what it was called. IIRC, Windows was moving to Git (through some virtual file system [0]) and had some major teams actively using it, but that was a while ago too.
