No one. Past-President Neal Crausbay has already explained it here - he was there and remembers what happened. I was there too, but I was just watching (and voting "yes.") All of those stories about Winchester and market share and all that - it's just a bunch of hooey. No one was trying to help any manufacturer, no one was keeping secrets, all that was made up to tell a story much more interesting - but less true - than the uncomplicated facts.
It was just time to get in step with the people who who knew what was going on, the technicians at SAAMI. They know how shells are made, what sort of standards are appropriate, and had devised the mechanics and statistics for testing them. There was not then - say 1992 or 1993 - anyone connected with the ATA with much understanding of any of this and it was clear where the future was (not black powder) and so we got on board.
Discussion lasted a no time at all and the motion passed with a comfortable majority. It was so quick, so non-controversial, that it never even made it into the minutes.