This is related to what you are saying, but I think the main reason is that the app has better user retention (push notifications, icon on your home screen). Also they get location data.
I worked at Yelp 2 years ago and can say that the main reason is definitely because web traffic is not reliable, it changes with Google ranking changes. And Google and Yelp are not good friends. They are super concerned with not dying if they stop showing up in Google.
