think of it this way: The search space for chess is much smaller, so we can lean very heavily on brute forcing in our A.I. implementations.
The search space for Go is much larger, so while brute force searches are critical in tight fighting, and in endgame play, something more has to happen to play go well in the middle game.
Chess fell to a much earlier generation of A.I. While Go held out until A.I. as a field had advanced as well several generations/decades as well.