There are definitely apps, which could be websites, e.g., using the coinmarkecap app doesn't make any sense in comparison to the website.

But there are many things which cannot be done sufficiently on the web, e.g., augmented reality, tracking gps in the background, accessing a users calendar or phonebook, Bluetooth, scheduled notifications, etc...

In general there is something called app fatigue. Convincing somebody to install an app is difficult these days, even if it's free... Let's see what the future brings for app development.