How can progress in such a narrow problem be representative of the efficacy of software either in some general sense or versus other narrow problems?

Also: what is the improvement over time of machine chess playing ability due to software changes once you subtract hardware improvements? I remember seeing vague claims that chess performance over the decades stayed fairly true to Moore's Law, i.e. scaled with hardware. As a lower bound this is entirely unsurprising, since naive chess implementations (walk game tree to depth X) scale easily with both core speed and number of cores.