Board Thread:Naruto Discussions/@comment-31480387-20170309081722/@comment-734582-20170313065801

Madara was the first man in modern times. Itachi didn't know about transmigration or Indra.

It's likely that each Indra transmigrant at some point awakened it, but since almost no history is kept of the era between Indra and Madara, it's unlikely people will know.