>> And why is that? <<
Only because the only records we have are the books he published. The witnesses are dead and buried for 600 years, and so therefore we have far less grounds for re-examining the evidence than we’d have for, say, Sacco and Vanzetti.
>> When was this doctrine first espoused? <<
Among Wycliffe’s Lollards, by 1380.
>> for the lack of priests this doctrine was formulated? <<
I won’t attempt to read Wycliffe’s or Hus’s mind. I can’t state WHY impanation was formulated. I can only state that it was a convenient excuse for explaining how it could be that according to Lollardists and Hussites there could be no grace among those they regarded as their opponents.
And Hus is dead, never given a defense under 'safe passage'.
Was not 'both kinds' the practice before the 13th century? Isn't this practice different than Christ's institution?