I've noticed this is particularly common on the Google Play store. Apparently the reason is reviews which go against what most people are reviewing are given a

I've noticed this is particularly common on the Google Play store. Apparently the reason is reviews which go against what most people are reviewing are given a higher priority and more likely to be shown to potential users. E.g. if an app is getting mostly 5 stars and you give it a 1 star, your rating will be more prominently shown in Google Play.