[dmitriid]

> And some random shell script installer is going to better than a dedicated package manager at dealing with the differences between N many distributions and M many architectures?

Surprisingly, yes. Especially for *nix systems where a lot of things (but not package managers) are more-or-less unified. The author may not have the time or desire to learn the half-a-dozen or so package managers and set up a build system to create packages for all of those, and then do the work of getting them into the standard repositories.