This is like complaining about too much biodiversity.
Accept that computing is a vast and complex topic, and that there are far too many ways of doing even basic things than you will be able to learn completely.
This does mean giving up the idea that you will be the master of the topic with all of the answers. It also means that you need to practice humility in the face of different customs. What can you learn from this strange distro? What does it do better than the tools you have?
Remember that your way is not the only way, and that it is statistically unlikely to be the best way. No matter how clever you are.
It's really not fragmentation. Each project serves a different set of users. They share the low-level concepts and technology, but differ quite a lot in methodology and higher-level details.
Specifically, it uses Nix as the underlying system, but implements a new syntax and maintains a separate package tree written in this new syntax. I'm not entirely certain why.
It's told very clearly on both the project's website and in the linked video that they consider the Scheme language to provide a more hackable interface for package specification and management. It's also demonstrated that it all integrates very nicely into Emacs.
On top of that it's also stated in the comments here, by a Guix developer, that while having a DSL for package specification is nice, they think having a whole general purpose language for it is better.
