Google updated its maps review policy on how to write & what reviews, and Google has the right to remove. In addition, Google has dropped Yelp's syndicated reviews from Google Maps. Upon checking several old map listings that contained yelp reviews just a month ago and now they're all gone.
Here's Google's public statement: "Place pages organize relevant information about a wide range of places and locations, and they surface great sources of information like reviews and photos about "places"ranging from restaurants to parks to landmarks to cities. Regarding the presentation of Yelp review snippets, neither of us was happy with the data as it appeared, so we reclassified results from Yelp while we reviewed our options. This means that, for the time being, Yelp pages mayn't appear as review snippets in Place page results, though relevant results from Yelp will continue appear in the "more about this place" section, which shows pages about a given location. We're working with Yelp to more intelligently crawl and present results from their site."