[jogsxyz]

There's more than one strategy available to the players. There's optimal strategy and exploitive strategy.

Let's say Bob plays a fixed strategy that's not optimal. Now Ann can adjust her strategy to exploit Bob's tendencies. This is still part of game theory.

Game theory is not a fixed strategy. Optimal strategy is a subset of game theory.

Bob plays a poor strategy. Ann can play an adjusted strategy to maximize on Bob's poor play. Then Ann can have +EV. The sum of Ann's EV plus Bob's EV plus the rake will still equal zero.