Apple and Google are able to gatekeep what you can install on entire generations of devices, from smartphones to tablets. Their power to gatekeep billion dollar markets needs to be looked at through the lens of antitrust legislation.
Apple yes. Google no. You can install 3rd party stores and freely sideload apps.
Google made it so third party app stores like F-Droid can't even implement auto-upgrading, or background installations of apps. App stores outside of the Play Store and 3rd party apps are 2nd class citizens on Android.
It is similar to how Gatekeeper works in macOS. Developers that didn't pay Apple $100 a year to develop and notarize software have their apps get treated like they're radioactive by Gatekeeper.