Simple - the programme makers don't want to make them!
They want celebrity gamers, and usual players such as women (how sexist), grandparents (how ageist) or priests (how stupid!) Why would any of these people be considered "unusual" ? Would they make a program about films, and ask for "unusual viewers such as women" - No! Computer games players are not (and have not) been this secular for years.
Oh - and this wasn't a hypothetical example. It really happened - as this bad casting call demonstrates.
Perhaps that's why there's no peep out of the makers since the call! Perhaps that's why every email has gone unanswered. No wonder! Perhaps every one saw through it as a Microsoft promotional gimmick. Perhaps people didn't want to be marginalised. Perhaps they don't care for people that use 'perhaps' in every sentence :)
However, if someone wants to make a good games documentary gimme a bell. Anything like Robert Cringeley's Accidental Empires for games would rock.
Any takers... ?