Apple has a monopoly on app distribution via iOS. Valve does not have a monopoly on app distribution via PC -- they compete with Microsoft, Amazon, EA, Ubisoft, Epic, Take Two, Activision, GOG/CDP, and so many other digital storefronts. I'm not understanding why Apple should be able to acquire such detailed market information on a totally different competitive environment.
If I were Valve, I'd be very concerned that Apple wants to get in on the PC gaming market, especially given all the rumors of a new Apple VR headset and controllers. Steve Jobs made a decision about gaming a long time ago, and Tim Cook might be looking to change direction.