Google has built a revenue generating juggernaut because they can create an auction around pre-existing intent. Essentially they have the hottest leads in history because they can deliver leads within a fraction of a second that the lead makes itself known. This leads to google capturing the majority of the profit margin for many transactions. For example if merchant X has $20 margin and merchant Z has $15 margin it would make sense for merchant A to trade $19 of margin to get the sale (this is why you hear so much talk about getting multiple orders from customers because merchants are willing to market at zero or even negative profit in hopes that they convert the customer again in the future). For a merchant with a recurring model it might make sense to spend 12 months of margin if their average customer stays 13 months. You get the point here, though, and that is that the real winner here is Google.
Similar dynamics take place on other advertising platforms, but if you are good at creating awareness you can make more money on the first transaction. The main advantage is that you aren’t in the muck competing against 10 competitors. I can find a potential customer and they are only presented with my brand.