Is content-based targeting really so much less effective than user-based, or is this more of an arms race between ad providers where even a small difference gives them a large edge? Youtube doesn't need to know someone is a snowboarder in order to show them snowboarding-related ads. They can just show those ads on snowboarding videos and they don't need to invade the user's privacy to do that. The targeting is not as accurate, but it's how ads have basically always worked, how they worked on the internet before the ad networks and tracking, and how they still work in other media.