It’s simple math. 97% of the population uses those two operating systems.
There isn’t much more incentive to go after the 3% Linux users. You know the population that loves free and open source software and isn’t exactly known for dropping a bunch of cash on software. Not to mention it’s a fragmented 3%. Even the flatpak, snap, app images of the world that were supposed to make devs lives easier are fragmented across distros.