One sibling dies, that's one less person to help take care of the family. District 12 is so incredibly poor that many families have to pull together to keep going, with older siblings taking out extra tessarae and so on. Especially considering that a lot of young people in District 12 likely do things to support their family, or at least, intend to survive long enough to go into the workforce and support their family.When it comes down to it, most people would rather struggle against starvation and perhaps live to see things get better, than have two weeks of fantastic food and then be certainly brutally murdered on national TV.

Katniss states in the first book that being a tribute from District 12 is synonymous with 'corpse'.If the tributes are really treated as well as they are prior to entering the Games, and there really is so many people starving in D12, why isn't there anyone volunteering? There has to be at least a couple kids dying of starvation and thinking something along the lines of 'if I go in the Games, at least I'll get a taste of what luxury is like before I'm killed, it's better than starving to death in the streets'?.

Fallout shelter avoiding inbreeding