Ratings and reviews cost money to maintain. Anti-spam, compute, distribution, security concerns, etc. Apple should do whatever they can to ensure that developers who aren't paying don't degrade the service for everyone else.
The App Store is already replete with terrible promoted software. Apple made an entire business around degrading the top search results so competitors can bid on less relevant suggestions: https://developer.apple.com/documentation/apple_search_ads
That would be a great argument if you could actually install apps from outside the Apple App Store.