Chess is a Perfect information game with a finite tree.
Very different problem than programming.
Very different problem than programming.
Entscheidungsproblem and Halt are not decidable in the general case.
While you have to find reductions, decidable problems having access to both yes-instances and no-instances makes it easier to find them.
I'd also suggest that our chess bots have evolved dramatically in that time. Deep Blue works very differently than AlphaZero, for example. Deep Blue might not be suited to code generation, but AlphaCode spawned from AlphaZero.