> Apple's messages app isn't really an app; it comes preinstalled on the phone, you can't remove it or substitute it with another app, and you can't install it on non-Apple hardware.
I'm not sure, but I don't think you can actually uninstall the default SMS from Android phones either without having another app installed at a minimum and then I bet similar to Messages if you were to somehow uninstall that app then the default app would appear since it's probably part of the core operating system (similar to other basic functionality like settings or a phone app to receive calls).
I don't know what you mean by you cannot substitute Messages with another app. If I didn't want to use Messages I would just disable all settings and remove it from the home screen and use whatever I wanted instead just fine.
You are correct that you cannot install Messages on non-Apple hardware. Not all software is open source or available for all platforms. For example I cannot install Playstation software on my Xbox, nor can I buy a Nest Thermostat and install a competitor's software on it (without hacking both of course). There are games that are made that aren't created with support for macOS. Etc.
> if you're part of Apple-oriented chat groups you can't switch to Android without losing access to those groups
What is an Apple-oriented chat group?
