You have an idea for an app. How do you build it? Your options generally are:
1) Do it the hard way: get Xcode/Android Studio, spend years learning to a) program, b) deal with the bloated and overly complicated frameworks, c) deal with the bloated and overly complicated build and deployment infrastructure. Also pay the platform owner for the ability to make it work / distribute it to someone.
2) Do it the easy way: pay some service so that you can make the app in a simplified/low-code way. Now your app is tied to someone else's service.
3) Do it the expensive way: pay someone else a lot of money to do 1) or 2) for you.
What's missing is the option 4): build it in some free, low-code tool, distribute it for free to whoever you want, without entering a relationship with any company whatsoever. That would be "the HyperCard for mobile".
On top of that, these days you're likely to want to have capabilities that are available only either through option 1), or through an API, requiring entering another relationship with some other third party.
Closest thing to 4) I've seen on Android is Tasker, with its ability to dump an .apk containing whatever UIs and if-this-then-that rulesets you created. But it's not exactly ergonomic, it's Android-only, and doesn't solve the distribution problem.