Ooooh. Got it. It's basically a way around the dependencies problem of apt-get, where this one requires This version of the library and that one requires That version of the library, and if you install this then that, oops, now it all breaks. Basically?
I'm guessing everyone also sorta panicked and moved to flatpack/snap when they realized how much apt's dependencies system left their ass hanging in the wind security-wise? That threat vector wasn't as recognized or worried over, early on.