That doesn't really make sense to me, though, since some pre-1990 players might currently be living in Florida or even further away from California.
I'm with Chris L. on this just being a simple oversight.
It may not make as much sense to you, but it's prolly a whole lot easier for the staff to get people from Southern (or even Northern) California. The less they have to worry about out-of-state contestants making accommodations, the better.
I imagine it's a cross between both that
and the show's relative obscurity. I also imagine you won't hear much from the Canadian or post-1984 versions (Orlando,
Big Deal, LMAD '03) for those reasons.