Can it be as simple as the same reason that the nevua that was transmitted is a tiny fraction of what there was. And the only stuff written are things that are nogeia L'doros..
I've been thinking and discussing that too...becsuse there were hundreds of true neviim that aren't in the canon.
Ovadiya saved 100 prophets alone.
Still, I'm not saying its not true. I said it doesn't make sense.
Maybe because I live in 2018 where we micro focus on every aged rebbe and rav but I can't believe that.. They visited aged taanaim and amoraim etc.
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i just don't understand how chagai who was a chain in the mesorah or Mordecai could exist for hundreds of years and this all not recorded nor were they contributing Torah etc?