On Android you have to pop open a menu and find the install option. That's not inherently discoverable as you need to know it's even possible, and most people don't.
It would be trivial to present the user with a more proactive notification that a site can be installed as an app, or even include such a notice in their search results on Google, but they choose not to do so.
It would be trivial to present the user with a more proactive notification that a site can be installed as an app, or even include such a notice in their search results on Google, but they choose not to do so.