Yelp plays by different rules
Yelp prohibits asking customers for reviews - not just incentivised asks, but any solicitation - and enforces it with a recommendation software that filters reviews it judges unnatural. This is the single most misunderstood fact in review management. A business that runs the same request campaign to Yelp as it does to Google will watch reviews get filtered into the 'not currently recommended' section, where they do not count toward the rating and are effectively invisible.
