in the book cathiching brand why do they each take the chance of offending those who will control the Games

Because neither of them really care anymore, they know they will most likely die and they have accepted it. They just want the capitol to be held accountable for once, even if it is just door them.

Because the victors are fed up with the Quarter Quell. The deal was that when they won they would never have to go into the arena again. However, the capital went back on its word and sent them all back to fight again. They are upset and angry and done with being controlled door the Capital and they don't care anymore. Because they knew there was only a 1/24 chance that they would survive.