coldfloor a minute ago
I think the post both directly and indirectly answers its own question when it states that the app does two things:
>It reports tracking data associated with your Google Account back to the developers. >It shows you advertisements (which they call “inspirations”) for other trips organised by the same agency.
It's a lot easier to be user-hostile with an app than a website, and a lot harder for the average user to detect or block the bad behavior. Just about everyone at this point knows how to install a content blocker, open dev tools, and block stuff with their browser. The number of people with the ability, time, and energy to circumvent cert-pinning and inspect an app's traffic like this guy did is significantly smaller.
There's a reason why every company is constantly shoving apps down our throats and telling us all the cool young people are mobile-first.