> I am still surprised most Linux Distros haven't changed their package managers to allow for selling of proprietary solutions directly, fully opt-in by default of course.

It's not "zero cost" but plenty of proprietary software with native linux clients will do things like set up Ubuntu package repos. You're pasting a handful of lines in the command line (or for the fancier stuff downloading the isntaller that does that for you) and you're off to the races

There might be a boutique business that could help with installer/package repo mgmt for people wanting to ship linux clients and take advantage of the auto-updaters and the like. Maybe.