An Apple Developer account is $99 a year and the only prerequisite to putting an app on the store. If it’s free, there are no other fees. I wouldn’t call $99 a small fortune.
There are many “open source” apps on the App Store, though most may argue they technically are not because you never have the option of compiling yourself, so perhaps “source available” would be more apt. Things like KDE-Connect are on the App Store so clearly there is some demand for iOS counterparts to open source multiplatform applications.
Not quite. It’s largely because a manager decided that an important metric for Google to be better at was “how much time users spend on the results page” which turns out you can game by just making the results worse so users have to stay there longer. Management made a decision to focus on metrics that are counter to what users would actually want because… well, here’s a better article that explains it:
https://www.wheresyoured.at/the-men-who-killed-google/