You really don't get how the human emotion plays into this, huh?
Happy to break it down.
iOS user installs your service's app. Android user wants to then install one-click Google Play Store, feels like a second-class citizen if they're instead directed to find a URL to log in, forced to create their own bookmark....
By focusing marketing on the App Store, and "Apps", which led to those goofy badges (App Store, Play Store, now Samsung/Amazon App Store sometimes), Apple made native apps "the thing". If you don't have those badges on your site or in your ad, you're not signaling you're "real".
But it's just a social trend, at the end of the day.
We can make the app's functionality the same, or better, wherever we want. Even in Safari gulp.