Git is a pretty much standard de facto for version control when it comes to the modern software development. Yet, there are still many projects, companies, and developers who don’t use it. Some, like WordPress, for historical reasons – it’ll take a lot of work to migrate all of the infrastructure and community to git. Others, for personal preference. An example of the latter is SQLite.
Here’s an interesting article on why SQLite does not use git. The core reason is simple – the main developer of the SQLite just doesn’t like git, and there is nothing wrong with it. But in the article there are a few specific technical reasons of why not git, and why Fossil.