The Google Play Store comes pre-installed on most Android phones, but there are situations where it’s missing, disabled, or broken. Devices from China, Amazon Fire tablets, phones running custom ROMs, ...
If you've been watching the news cycle around app bans and the policies around what is and isn't allowed in the app stores run by Apple and Google, you might have also seen references to "sideloading" ...
You're not stuck with the Amazon App Store.