It's a diplomatic relations things.

The point of the Olympic isn't actually to find out who's the best, it's traditionally a way to get all the different countries together in a friendly non violent competition to encourage positive relationships with each other while showing off the best we've got.

The way they choose the city that hosts the next games is decided by a committee that also has to consider the fairness of how frequently certain countries get to host and that balance because in spirit the Olympics doesn't belong to anyone. I think there are actual criteria about the selections but I'm not certain what they are honestly.

If China didn't get to host the Olympics it would've been a serious disrespect to them as a nation, one that goes beyond just cheating or anything like that.