Reddit (for example) would have a perfectly fine mobile web experience except that it harasses you to install a mobile app that is worse than the web site. (Ought to have a steaming turd emoji next to the "call to action")
The app experience is almost always worse than a web site unless an app can take advantage of some special features of the platform such as high-precision locations in the Apple ecosystem.
The bad experience drives people away the same way the ads drive people away from OTA TV.
I think the real reason sites like Reddit want you to install their app is that they can't both have fancy JS and speed.
Web browsers are ridiculously complex and slow, and slow means bad UX. An app is much simpler (and thus faster) than a JS-heavy "web app" on Chromium/whatever (which is many millions of lines of code).
HN is fine with just a website and doesn't need an app because it doesn't have fancy JS.
It's open sourced and you can use it from https://yahni.news
I don't know what problem an app would solve in this case.