[adar]

What else would you call the Play Store on which the vast, vast majority of Android users acquire apps? Please don't bring up F-Droid or the Amazon App Store as alternatives, that's just a joke compared to the sheer volume of app installs (and more importantly, purchases) on the Play Store.

[breakfastduck]

Just because alternatives are not as popular as the default store does not make it anywhere close to being a walled garden. I'm not sure you understand what the term means.