Literally most of the packages on the page you link there explicitly say that they're maintained by other people. The author seems to maintain an RPM and a DEB setup, which is already more than most. And my point is absolutely not that some people don't go nuts there, but that's not where or how most Linux users get their software. It's mostly coming from stuff packaged by the distributions.

And I am sure that's how most open source packages on Linux are built. Again, I spent a lot of time in that world. (Former KDE core developer, former employee at SAP Linux Lab, friends working at all major distros, have a bunch of my stuff in every distro, talks at lots of Linux conferences, etc.)

Building really isn't the problem. It's testing and supporting. Building is relatively easy. But you can't just ship commercial packages without testing them. Pulling out a Debian 11 VM because someone's having problems with your software there under Wayland, but not X11, but it seems to work in Sid... Again for the 0.01% of your customers using that configuration, ... it's hard. And it rarely makes economic sense unless you've got a disproportionate number of users on Linux, or a ginormus user base. You can't assume because something works on Arch Linux that it also works on Mate. Or that something on Ubuntu works on Debian. Or Redhat on SUSE. And then your users may have any of 3-4 versions of those installed. By the time you get to a specific configuration you're dealing with often debugging things for a single-digit number of users.