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Why isn't there a CoolStoryBob smiley on the forum?
What is the purpose of paid tournaments? Logically, it's to win money. In poker, anyone can win with a bit of luck (there are many such stories), but in Heroes, only a few players initially have a chance of winning, and these are usually the same players. Regular players will quickly get tired of investing money because they can play in free tournaments anyway. Without amateur players, tournaments become less profitable for professionals because playing against each other over the long term will result in approximately a zero-sum game.
As for duels with bets, you can always agree directly without intermediaries.
Regarding sponsored tournaments, the situation is different, but sponsors haven't stopped investing money in Heroes. However, there is a positive trend in this direction.