Reviews are one of the primary ways that the Google Store evaluates and ranks the apps on the market. Google services are largely automated, so the goal of increasing your Android ratings is to prove to the algorithm that your app is increasing in popularity.
Google's AI is constantly evaluating both app reviews and app downloads to identify trends. If your app gets lots of reviews in a very short period of time, the AI will see that as a surge in popularity and begin app promotion on your behalf. One of the primary ways it does this is by increasing your app's rankings in the store.