I’ll give two reasons. First, code bloat, expo bundles allllll their default libraries along with your app when packaged for release. Second, is flexibility. The most powerful part of react native is that it displays native views and with expo you are only given the native functionality they bundle for you, you cannot create your own.

The alternative is to just not use expo and add libraries as you need them. Then you can do things like add widgets and watchOS functionality to your app on iOS using native code. Or create your own custom native views and plugins that bind to the native sdks, giving you an edge over other bland RN apps. I love RN but only when used correctly.

If you do use Expo, you should eject as soon as possible and pick which libraries you explicitly want to include. I reduced my app size by like 60% after ejecting because of all the stuff I didn't need that was included.