There are probably multiple factors driving this. I think Match Game is the only thing that's from the 20th century that GSN airs right now.
It's also one of only four(?) shows that aren't GSN originals (Deal or No Deal, Cash Cab, and Feud being the others) so I'm guessing there's interest in keeping more of the programming in-house. Also, with Press Your Luck and Pyramid returning to the ABC schedule, having the Great Valu versions of those shows on GSN's schedule lines up with our perception of their programming ethos.