Most customers of Adobe and Affinity are on Mac or Windows. I am not sure about Windows, but unfortunately GTK apps are absolutely horrible on macOS. It probably makes more sense so fund something Qt-based for better cross-platform support.

That said, for big companies a Creative Cloud subscription (let alone a single app subscription) is only a drop in the bucket compared to employee salaries.

I think Affinity Suite is probably most popular among indie folks, people who need it less regularly, etc.