Quick answer:
Becuase there's not much to tell when the main cast is dead, is there? From the times they actually told you what happened after, ie. Himatsubushi-hen or Yakusamashi-hen, there isn't really much to tell besides the aftermath. Ooishi/Akasaka still couldn't solve the mystery, have tons of different theories, and still doesn't know what was the cause of the disaster, the truth about the 5 years worth of disappearances/deaths, nor who was the real culprit.