If the kai’sa story is accurate, that sucks.
Prize splits are a longstanding and accepted part of competitive TCGs, poker, and many other competitive games. Players are free to enter into whatever agreements they feel are best for them. Whether or not you personally choose to split is beside the point.
The integrity of those agreements matters. Reneging on a split after learning you are the winner undermines trust and damages your reputation. If your word isn’t good when money or prizes are involved, people will naturally be hesitant to make future deals with you.
And for those saying “just don’t split” not everyone is in the same circumstances. Some players split to reduce variance, cover travel expenses, or for other personal reasons. You don’t have to make those choices yourself, but that doesn’t mean those who do deserve to be taken advantage of.
A little empathy goes a long way.