It's not a game people want to play.
Magic: The Gathering... they made sort of a one off rubbish I wouldn't play either and that saturated that market. Making more and more variants under different name won't magically bring more customers.
Valve had Half-Life and then Steam, the rest... what rest... not worth mentioning really. It was either a mod or bought from elsewhere.
Valve will sit on Steam until they keel over. All their explorations into AR, VR, ... some games no one wants to play... just a money dump.
HL3 that people want they do not want to make because they would need a damn good writer and team to build it, neither of which they have anymore.