I think it's more than that. It's a walled garden. If you want to leave go somewhere else, it's further away than just a tab. That increases stickiness.

For example, let's say I'm an airline. I don't want you in the browser, where you're going to have my competitors in the adjacent tabs. I want you in my app, where all you see is my version of the world. (I mean, yes, you can have multiple apps open, too, and switch between them. It's still a bit more friction than moving between tabs. Or maybe that's just my mental model, and young people see apps as just another kind of tab?)