i don't know. it's mysterious that nobody even came up with the algorithms for decades, which often do still work well on toy examples. MCTS is the kind of thing people definitely could have thought of at any point since 1950; and neural network value functions for board games had already succeeded with TD-GAMMON.

this is even more striking in poker, where counterfactual regret minimization wasn't invented until 2007, despite being a relatively simple algorithm to describe and all the essential intellectual building blocks being known since the 1960s.

von Neumann had invented extensive form games with the express idea of modeling poker; there were researchers in the 1950s/60s (Hannan, Blackwell) working out the core ideas of regret minimization. One innovation (the sequence form representation of game strategies) was only known in the Soviet Union in the 1960s and not propagated to the West. But this was independently rediscovered in the early 1990s and it still took another 15 years for CFR to be developed.