I’m guessing the reason for most things forcing you to use an app is less because of data harvesting, and more because it increases repeated use.

When you have to go to your browser and remember to check a website it’s harder to create a habit. If you have an icon flashing on your home screen every day it’s much easier to remember to go to their site. Sure you can “Add to Home screen” functionality, but average users don’t even know that exists.

It also feels like a bespoke app is more “professional” than a website, despite many apps secretly just being a website anyway.

That said, they are definitely harvesting your data. I just don’t think that’s the main reason for most apps.