Imagine a fully statically linked version of Debian. What happens when there’s a security update in a commonly used library? Am I supposed to redownload a rebuild of basically the entire distro every time this happens, or else what?
This was indeed comon for Unix. The only way to tune the systems (or even change the timezone) was to edit the very few source files and run make, which compiled those files then linked them into a new binary.
Linking-only is (or was) much faster than recompiling.
If you're a an indie developer wanting your application to run on various debian based distros but the debian maintainers won't package your application, that's when you'd see why it's called DLL hell, how horribly fragmented the Linux packaging is and why even steam ships their whole run time.