I don't know. Typically the 5950/7950 is not targeted towards gamers. It sacrifices single core performance for more cores. Usually it's more of a prosumer audience that actually do need those attributes.
Yes the 5900/7900 but those have 12 cores. The higher end 5950/7950, which has a higher core count, actually perform slightly worse in games and are targeted towards a prosumer.
Don't get me wrong, they still work amazingly well for games. It's just that they sacrificed some performance in those chips for the higher core count so it only makes sense they'd want to push that further.
But my guess is they don't want to compete with their threadripper line. Unfortunately those come much later in the product cycle so we'll probably be waiting some time for a Zen 4 threadripper.