Social proof ( in this case user's feedback) is a major factor in the psychological game of influencing people to buy your product, idea or apps. On the app stores 75% apps are free and 60% are not rated.
During a normal day, every mobile user comes across five to six push notifications or advertisements on their phone. But do they click on all of those ads? Let me rephrase that. Suppose, you're shown 3 different mobile ads about an offer on Apple products, a trailer of the latest Game of Thrones episode and a UEFA EURO 2016 commercial by Adidas. Which one will you click on?