[tellyblues]

The odds on the same contestants appearing will be higher if producers want to cast people who are proven to be comfortable on TV and will probably have a good grasp of the game. Most "normal" people don't have the luxury of a life where they can just give up their responsibilities to appear on a gameshow so it's going to be those who do and contestants who make a living out of TV are in that category. There are also blacklists at production companies with regards to contestants so that narrows the list down even further.