Google gets much more traffic, supports the customer review process, and has a much better reputation among local businesses than Yelp. Since anyone can leave a review from any account, it's easy for your customers to review your company. Although Google is rapidly dominating the online review landscape, it's still less competitive than Yelp, Facebook, and other online review platforms. If you leave a review on Yelp for a tree service company, the likelihood that you'll see that review again is very low.
Whereas a couple of years ago Yelp was the leader in aggregating online reviews, Google has quickly overtaken it and has become the most popular review source for consumers.