Here's why:
* The Tournament is about glory, not money: The Triwizard Tournament is primarily about prestige and demonstrating magical skill. Winning schools and champions gain immense glory, and the reward is likely seen as that recognition.
* No mention of prize money: The books and movies never mention any financial reward for winning the Tournament.
* The focus is on the challenges: The emphasis of the Tournament is on the dangerous tasks and the challenges faced by the champions, not on a monetary reward.
So, while it's possible that there could be some prize money, the focus of the Triwizard Tournament is definitely not on financial gain.