Search is probably the most likely counterexample of your rule. They can sell ads based on search terms instead of user profiles. This might be leaving some profit on the table, but might not.
They can generate artificial scarcity by preventing the search query stream from being joined to user profiles by third parties.
If they end up with a well-educated, affluent userbase (likely, given their selling point), they can charge a huge premium for that scarcity.
This trick is much older than the internet itself.
They can generate artificial scarcity by preventing the search query stream from being joined to user profiles by third parties.
If they end up with a well-educated, affluent userbase (likely, given their selling point), they can charge a huge premium for that scarcity.
This trick is much older than the internet itself.