One thing I haven't seen addressed in the post or comments (sorry if it's there and I just missed it) is for apps and websites that sell non-digital goods to customers.

For returning customers, a customer with an app installed is simply going to have a lot less friction to open the installed app and place an order than a customer who has to open their browser, log in again, and then place the order.

That alone is worth the investment for many companies in making an app, even if a minority of customers actually choose to install the app and keep it installed.