Personally I believe that niche products are the way of the future and that general platforms (Facebook, Yelp, etc.) will not last in the long run. But from what you described I don't think you made this (implicit) assumption clear, and it's not clear whether that's the sort of business they want to invest in (in the short term, the general platforms will be where the money is made, and it will be the aggregate of the niche platforms - a much more profitable investment than a niche product).
Personally I believe that niche products are the way of the future and that general platforms (Facebook, Yelp, etc.) will not last in the long run. But from what you described I don't think you made this (implicit) assumption clear, and it's not clear whether that's the sort of business they want to invest in (in the short term, the general platforms will be where the money is made, and it will be the aggregate of the niche platforms - a much more profitable investment than a niche product).