You can see the installed downloaded binary, sure. And you can see usage after the fact, but there is no reason to assume that the app store size is the only download it will use, most major apps I've seen use a lot more even when not downloading media.
Option A: Only runs on one platform, can only be published on that platform with the blessing of the manufacturer of your device and little-to-no insight into data usage
Option B: Cross platform, can be interfaced with using open standards and block parts of it that you want (not just on a DNS level, but on a resource level)
You prefer option A because it’s much better experience.
If you’re building a service that’s not suitable for option A then you use option B. It’s not really a discussion at that point.
I’m glad that there’s an option B the way that I am glad that there’s frozen pizza in the fridge. Good to have it but I’m not gunning for it if a proper restaurant pizza is available.
For websites, this is not an option.