But that's why there's no real need for manipulation. App store what highly rated apps and app makers want their apps to be highly rated so they use more or less dark patterns and incentives to incite users to leave good reviews.
There's a massive selection bias at play which tends to naturally inflate review scores without any explicit fudging.
I thought that at first, until I considered that user ratings might not actually map all that well to things like how long they spend in the apps, how likely spending time in an app is to increase their time spent in the store or on their device overall, and/or how much money they spend in these places.
Or, even better, high ratings for apps from large corporations encourage them to support the continuation of your store's monopoly power.