"The participants of the agilemanifesto have been known beforehand"

Actually no they were not. Most had been blogging and they knew about each other. But the first time that the larger IT community heard about any of them was when eXtreme Programming Explained was published by Kent Beck.

The members of the Agile 2 team were deliberately chosen to be people who were not invested in the status quo: not established Scrum trainers, etc. We wanted people who were not beholden to the current regime.

BTW, I was known beforehand. Prior to Agile 2, I had written three IT-related books - one was a bestseller. And I had created an IT company that grew to 200 people in five years. Others of the Agile 2 team are also quite well known, e.g., Adrian Lander. But again, we did not want people who already had "something to sell".