They are not doing it for the $10 admission, they are doing it to get the $500-$1000 or more purchase of tickets.
It is very hard to get people to donate larger amounts of money to a charity especially one they are not involved with. A Chinese auctions tends to attract people not normally involved with that charity.
Also it draws attention to your charity and maybe get other donors to come.
I went to a chinese auction for TAG, I have nothing to do with them, but the auction was held at the inwood country club with the best Sushi ever!!!!
I can attend such an auction