My answer may not be accurate enough. Doomsday novels usually referred to a fictional science fiction novel that described a story in an apocalyptic era. Such novels often involved the exploration of human nature and the survival and struggle of humans in extreme environments. If a million-word apocalyptic novel wasn't on the novel rankings, it might be because it wasn't popular enough or didn't appear on the rankings. However, this did not mean that it did not exist or was not worth reading. Many post-apocalyptic novels were very popular and highly praised after they were published. Therefore, if you like this type of novel, you can try to read some different works to find your favorite style and theme.