In the US, they're the shady back-alleys of the Android world. Other non-Google Play Android app stores exist. Here's what you get when you search for best-selling Android game Genshin Impact in Amazon's app store. Look at Microsoft itself for why: The official Windows app store has always had the entirety of the Windows 10 install-base to serve, and it isn't great.

The best possible outcome of this is that the huge new audience of potential Windows users will revitalize the Amazon Appstore and lead app developers to put their products in there.

But when something awesome comes to Android, it often doesn't come to the Amazon Appstore. Those specific apps aren't a big deal on Windows, which has its own apps or terrific browser-based versions of those services. The Fire HD 10 productivity bundle got absolutely slated as app after app wasn't available on the Amazon Appstore-Signal, Slack, Rome2Rio,, Google Sheets, what have you. I saw this when reviewing Amazon's most recent line of Fire tablets. That makes Google's app store the default and often the only choice for most Android app developers. Although Android is an 'open' platform (unlike iOS), nearly every Android phone outside China comes preloaded with Google Play. But Microsoft can't get around Google's absolute, crushing dominance of the Android app world in the US.