Because it is two orders of magnitude less effective. Putting an ad for a blender in front of someone recently searching for blenders is 100x more effective tha

Because it is two orders of magnitude less effective. Putting an ad for a blender in front of someone recently searching for blenders is 100x more effective than putting it in front of a random person. This means the revenue they can charge for that ad is 100x less, which means that any sites without massive, massive user bases will perish, and those that survive will do it on a pittance.