I think this is true, but there is rational for why you would sell the data even if the data is good. On a hypothetical scenario, say there was a great app for

I think this is true, but there is rational for why you would sell the data even if the data is good. On a hypothetical scenario, say there was a great app for checking price comparisons for some esoteric product, or even say televisions. People download the app, and use it in Best Buy, etc. to compare tv prices. The location data therefore might be high quality/relevancy in one situation, but have low frequency and use to be valuable as a single source for advertising/selling to a hedge fund. Therefore, there would be hypothetical value to a data vendor aggregating and normalizing all these small sources into one feed. In practice, the level and quality could vary significantly, and the difficulty to normalize the feeds could be much harder in practice. If you get data in aggregate from Foursquare and Yelp, potentially it can tell you enough to gauge foot traffic in restaurants, but to your point, it probably can't be used to build an advertising platform.