As opposed to the publicly available Google Trends data? As opposed to running legitimate market research? Wouldn't you rather know the most searched person in your vertical, market, etc?

The data in this example was going to be made public anyways. All the examples of prediction markets are predicated on them becoming public. You not only need the info, you need the info before it becomes public.

It's not always enough to know what - the why is often important.

For example, d4vd is a famous musician, and search stats may indicate his potential popularity and future record sales.

Or the public may be searching his name to find out more about the body found in his car, and the subsequent murder investigation and arrest.