I could put "aviation" as one of my interests but I'm nowhere close to being able to afford a plane or any aviation related accessories unless they're R/C models (even then that's pushing it).
Just because I see ads I'm interested doesn't mean I'll want to buy what they're selling. Whereas if a system that tracked me can deduce that I'm a private pilot, it can make an educated guess towards my income and adjust the type of items it shows me correspondingly. I doubt many people would be willing to provide this information (demographics, location, income) that advertisers care about most.
Just because I see ads I'm interested doesn't mean I'll want to buy what they're selling. Whereas if a system that tracked me can deduce that I'm a private pilot, it can make an educated guess towards my income and adjust the type of items it shows me correspondingly. I doubt many people would be willing to provide this information (demographics, location, income) that advertisers care about most.