1. It's not unique to the play store, as a matter of fact, this started in the iOS app store and was "adopted" by Google. It could definitely be improved though, i.e. if all potential in-app purchases were listable via the store page, like on steam for example
2. The prices were mentioned in the comment you're responding to.
Where? Just checked on every app I've purchased in app unlocks and none of them have any indicator for these unlocks (or others that are still available) on their app store page.
The only way to see them - from my experience which I just verified - is to go into the app and go into the relevant menu's of the apps.
Please explain where you're able to see this information on the app store on iOS or iPadOS
Is this maybe only available for some regions or opt-in for the developer? I this UX doesn't exist on my devices running on 26.2 in the apps I checked. I just verified again but no luck
/Edit: found it! that is way too hidden - Would never have found that without your explicit mention and gif link!
After exploring some more on the play store too, There is actually a similar UI in the app details there too, it doesn't list all items but the price range (cheapest item to most expensive item). Definitely worse then having all items listed, but both could be improved imo by listing them as repeatable purchases, temporary licenses, forever unlocked etc) for informed consent before install. I'd never install any app which has repeatable transactions for example
2. The prices were mentioned in the comment you're responding to.