And what if your goal is to distribute software to users that may be running any arbitrary OS? You can't tell them "install Guix, learn how to use it, then use Guix to install my app". You'll lose a lot of users that way.
At the end of the day, users care most about getting stuff done. I am the author of a popular app that is written in C++ and uses Boost. Many users literally begged me to bundle Boost because installing Boost is so much of a pain for them.