Very few other sources aggregate information in such a nice way as them. I'm unlikely to find any article from other sources listing the cause of death of all Congressmen. Wikipedia does link to source material, and even if they didn't it is easy enough to check, if they really think nobody in Congress dies of cancer. And many of these deaths are pre-Q, so people are well less likely to say "but It says John McCain died of cancer, but we know that traitor got hung".