As far as I'm aware it only became obvious to people after the Dimond brothers broke the story, for which no one gives them credit just like so many converts to the true faith came through them but won't acknowledge it after they reject EENS dogma.
You are right here. The first time I heard this was from the Dimond Brothers. My initial gut reaction was that it was a kooky conspiracy theory--like all the others. It was actually after realizing that the difference between a conspiracy theory and the absolute truth so often
time that I relooked at their presentation and decided that they were making some really good points. I have never heard why Chojnowski decided to get involved in the matter, but his organization has pretty much definitively proven the case.
As a side note, the time between "conspiracy theory" and "truth" seems to have shrunk over years from decades to weeks and sometimes even days.