As what others have said, it's mostly due to FMA. To a lot, FMA would probably be their first dive into the genre. I know when it first started airing on Adult Swim in it's initial run, it definitely had a different feeling to it than what I was used to seeing. There was something compelling about the show and it was one you could actually attempt to recommend to people who never got past "anime == that dbz cartoon"
And it was really well acted too. Despite there being good dubs of shows before it, FMA hit the right sweet point in time where all dubs were increasing in quality, so I'm sure many attribute that show as "starting it all."
So that's my theory on why. There were plenty of actors involved that made that show though, outside of Vig, so why some of his stans think he made that show is beyond me. Sure, he plays one of the two titular characters, and I won't deny the significance in that, but Alphonse was just as important. FMA was a package deal. It wouldn't have been as good as it was if it was just Ed. It actually speaks volumes of the original manga author's writing ability, in my opinion.