That's not quite true either. Because an app installed like this will only function for a very limited time (a few weeks i believe) and then it expires and you can no longer start it. This means it is not practical and NOBODY will use this: which explains why there are none/hardly any of such apps available on Github, etc.
I did this with the f.lux app in the past and it was very annoying/not usable because of the necessary "recompile frequency".
Though I guess most people may just want to throw their arms up and force the government to write a law to make such easier for free?
Haha, no. Last I did this, you must have a Macbook, you must configure Xcode, generate new certificates, sign the entire application bundle, and then you get to sideload it - and never get an update ever unless you repeat the entire process.
In contrast on Android: "This application is from an unknown source. Would you like to still install it?"
Technically you just need macOS, I don't think there's anything stopping you from doing iOS development on a hackintosh.
I'll agree that the process is pretty ridiculous in comparison to Android though.
This is not quite true. If you write your own app you can install it on your iOS device. If someone put an iOS app on, say, Github, you could easily install it. No need for the App Store or Apple's review process. An app does not need to be signed unless you want to submit it to the App Store. Also, you can install iOS without using the App Store if you have a developer account.
I'm not disagreeing with you that iOS is far less open than Android.