Having a desktop app is great, but unless you have admin access to your desktop, few are going jump through the IT hoops to get it installed.
Whereas Windows Store apps don't need this permission. Having the desktop app available through the Store would widen adoption.
@Nick Bryant - Windows users have the ability to install the desktop app on a per-user basis without IT consent. However, currently, Mac users need to go through IT to install the desktop app or update to the latest version.
Our Product and Engineering teams are looking into improving this experience for Mac users too.