PorkrollPosadist nailed it, but if you need another framing it helped me to think of NixOS as learning an entirely different OS as opposed to trying out a new distro. That declarative config is an abstraction of the underlying unix OS and the software available for it, and a lot of the techniques you know for managing a unix system don't work on that abstraction.

The learning curve is painful but so worth it for desktop portability or managing your homelab.