I think the illusion of "cheap" confuses most marketers. Marketers are left with an unbalanced sense that they are getting higher bang for their buck, ignoring centuries of marketing best practices about expanding reach and exploring non-traditional targets for secondary/tertiary effects. But I think it works well for the ad platforms themselves in the way that it encourages whales just like microtransactions in games. A marketer has an easier time considering opportunity cost for one big ad spend, versus not even paying attention to opportunity cost as they buy a lot of individual micro-targets. (And relatedly not paying attention to how much they are over-spending on people that already have their message versus missing opportunities on greater reach.)