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There's a lot more selection criterias (the first one is the median of the percentage of the votes' rewards made after 30 minutes). Then a "score" is calculated taking in account this median, the median of the number of votes before attaining 1% of the total post rewards, and the median of the time it takes to attain 5 votes. And it's this data (and some more) that determines a score of profitability for an author.
But it sure excludes some high profile authors like haejin for example who isn't profitable except if your vote weights a LOT. But the goal is to maximize the ratio Value of the vote given / SP received from curation.