Just curious why in China there are several app stores for Android (Tencent, 360, Baidu etc), while the rest of the world uses mainly Google Play Store?
The Google Play Store is outside the great firewall and therefore probably unusable in China. Phone makers aren't going to ship phones with unusable app stores, so they need to use alternatives. It's the same reason UC Browser and QQ Browser are so popular in China.
I'm curious why there aren't more app store outside China, as evidently from China example, the app store business is sustainable, and Android outside China has a bigger market.
Samsung, Motorola, Amazon, etc. have tried. The trick is to convince all the developers to publish on your app store, so the users will use your app store. They're not going to bother if the phones also have the Google Play Store. The phone manufacturers need to include the Play Store or users won't buy the phones. There is a large first mover advantage.
Play Store is the default app store on essentially all Android devices aside from the Amazon Kindle Fire. Adding a third-party app store involves enabling sideloading in the system settings and manually downloading an APK. Why would a user go to that effort, when essentially all Android apps are already available on the Play Store?