Legitemate question - why can't apps give simple cost breakdown when users are purchasing stuff from within the app? If I let's say topup credits used for micr

Legitemate question - why can't apps give simple cost breakdown when users are purchasing stuff from within the app? If I let's say topup credits used for microtransactions for $10 from within an app, user will pay the price, which subtracted by 30% of it's value will equal 10$ - in this case 14.28. Unlucky users who don't know about possibility of purchasing same stuff let's say from the website will pay and forget about it, lucky ones will go to the website, pay $10 for the same thing and understand why is the difference (apple tax). This is simple transparency which actually is present in US when people are paying the price + tax, unlike Europe where people are seeing price with tax included. Am I missing something here?