UWP's appx format is awesome - one click installation, sandbox, clean uninstallation, potential for diff updates. All these have nothing to do with portability.
But they crippled it by making it store only until recently... Too late.
One reason I hate using Edge is because i like chrome and Firefox, it's impossible to install extensions from the browser.
Why can't I use the store through my browser? There's absolutely nothing stopping the store from acting as a downloader and installer in the background.
If the store worked from the browser, usage would pick up.