Data harvesting isn't about trying to find saucy details about you that can be used against you like blackmail. It's not about whether someone has "nothing to hide."
It's so corporations/advertisers/influencers know your routines, know your interests, know what kinds of content you respond to, know where you get information from, etc. in order to use those avenues to influence your behavior. And advertisers just using it to sell you a product only scratches the surface. What they really want is to know exactly what lies they can tell you and how to dress them up so that you'll believe them without question.
This is what was discovered when Cambridge Analytica blew up years ago. And then, by some "miracle," it was almost completely forgotten within a year of occurring, and no meaningful actions were taken to prevent similar threat actors from manipulating people again. And yet we are seeing dozens of examples in recent years of deliberate misinformation campaigns being used to influence global politics, all because people believe it's okay to freely give up their data because they have "nothing to hide."