The idea is that you do not install packages, at all. Instead, you would use Flatpak and the like, plus mutable containers (Distrobox or whatever) if needed.
Ah yes unlike other package managers that magically make applications not need dependencies.
I can think of two explanations: (1) Debian packages have more shared parts, and (2) they have optional dependencies ("recommends" and "suggests") which I disable by default. Because of (1), there will be many library packages to download, but the overall volume is reduced.
They become necessary when you are dealing with Windows style "applications" that drag in enormous amounts of dependency. I had Libreoffice fall over on Void Linux because of some JVM issue. You think I want to debug a JVM issue in 2020-something to type some text? No thanks - flatpak.