I think brand ranking works in the way like how trending works on twitter. If your name is being searched the most or more articles regarding you are appearing, you will rank higher. This helps company greatly when their idols are within the brand ranking, since it'll bring in more CF offers, dramas, movies, etc. It also helps the idol or actress/actors themselves. Essentially it shows the popularity of the person during a certain time period. That is why we see different celebs ranking every time, depending on if they had a movie coming out, new shows, comeback, etc. I think another way to look at it is if the amount of commercial deal a person have within a period of time. Those are my guesses.
So if you have huge fanbase and all them fans search via your name...you get the point.
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