The average user might have one or two non-free programs they depend on that aren't websites. Maybe AutoCAD, or Photoshop, or SketchUp, or Excel, or the driver for their oscilloscope, or Dark Souls. Everything else can easily be free software or webapps. So an "app store" that doesn't contain non-free software can be the primary source of software, and for almost all Debian or Ubuntu users, it always has been.

The average Ubuntu user doesn't even have those one or two non-free programs. After all, Autodesk doesn't provide a version of AutoCAD for Linux in the first place.