1. Persistence: while websites are very easy to close, deleting an app is much more difficult and usually requires pressing on some “red buttons” and scary dialogs. It also makes sure the user now has a button for your app on their Home Screen which makes it a lot more accessible.
2. Notifications: while they exist for websites too, they are much less popular and turned off by default. Notifications are maybe the best way to get the user to use your app.
And while I hate the dark patterns some companies use (Meta, AliExpress, etc), I do understand why installing the app worth so much to them.