Scale effects? To be popular, you need large database. It took Yelp years to get there. It will take another company years too, but now their risk is much large

Scale effects? To be popular, you need large database. It took Yelp years to get there. It will take another company years too, but now their risk is much larger since there's Yelp already which dominates the field. So company founder has to get somebody to invest not in just developing a new field for years, but in developing for years a field where there's an entrenched and popular (even if shady) competitor. Ultimately, I guess, if Yelp continues to be shady, it will pop up, but may take a lot of time until it's useful.