Barney Frank is desperately raising money to defend his seat. Jim Oberstar and John Dingel are worried. I can't see any of these guys losing. Yet... There's been a poll released. Maybe some whispers on the Internet. There's a chance the congressman in a seemingly safe district could lose. Congressmen who've never worried about re-election panic. They don't know what a competitive race looks like and, well, this is a Republican wave year. Who knows? Maybe there is a 10% chance he'll lose.
So Barney Frank concentrates on his own re-election. He isn't helping other Democrats. He's raising money, contributions that could go elsewhere. The DCCC redirects money to save a chairman's seat. If Democrats spend money in seats where they are 90% likely to win without spending the money, Republicans have a better chance to pick up actual close races.