It's clean, powerful, and elegant, so you can spend most of your time coding, not adding lines to an unreadable, unmaintainable Make (Or CMake 2) file.
Build systems is a hot topic. Of course there are many options. But even a really good one, or one that re-uses a familiar syntax, can't come close to CMake.
Every IDE supports CMake (or CMake supports that IDE).
More packages use CMake than any other system.
So, if you use a library that is designed to be included in your code, you have a choice: Make your own build system, or use one of of the provided ones, and that will almost always include CMake.
And that will quickly be the common denominator if you include multiple projects.
It's easy (1-2 lines in many cases), and you'll find that 5 minutes of work will save you hundreds of lines and hours of CMakeLists.txt writing, and will be much easier to maintain in the long run.
This book tries to solve the problem of the poor examples and best practices that you'll find proliferating the web. A nice, slighly dated post with a similar intent can be found [here](https://rix0r.nl/blog/2015/08/13/cmake-guide/). You might also find that helpful for a fast introduction.