Not always. The idea here is that an app would be able to use some of the phone's native features, making the user experience more straightforward.
Think about the camera purchase concept. If you open a website, once the user has selected a product, they have to either login or enter payment information (like a new credit card). But with a native micro-app, it can just start a payment intent that accepts whatever the user has already saved to their OS (through Google Pay). Basically two taps and you're done, as opposed to a bunch of taps and filling some forms.
Much less friction, if done right. And that's just one example. I'm sure people will come up with others.
I'm sure some publishers will want to abuse the system to force people to run apps that have no benefit over a simple web page. Same problem contrived "mobile" websites have. But at the same time there's a lot of micro-situations where mini-apps serve the user in a much better fashion.
At least until HTML5+ has proper APIs for the features they need.