The basic function of an injection mold is heat exchanger

The undeniable, basic fact is that no-one really WANTS to have to purchase an injection mold. It is the plastic parts that it produces that are wanted and that generate revenue to pay for either the injection mold that made them, or the next mold. Strip away all the technicalities and consider the basic function of an injection mold - it is nothing more or nothing less than a shaped heat exchanger. But that heat exchanger ideally would:

be at exactly the same temperature as the material when it is injected into it;
only extract heat just when you wanted it and no sooner (at point of fill);
extract heat thereafter at a rate commensurate with the heat load at any given point and with the characteristics of the material;
produce plastic parts that precisely match the design intent, with absolutely no process-induced internal stresses;
run at the shortest achievable cycle time;
eject the parts with no difficulty and without marking cosmetically important areas; and
never wear out or need maintenance;

However, it also MUST:

be capable of withstanding 2,000–3,000 bar pressure generated by the gooey, highly compressible stuff called plastic that we force into it;
be manufactured by machine tools that have major limitations (fracking drills may turn corners, but water lines made by drilling have to be in straight lines). Conformal cooling is (rightly) becoming more prevalent, but remains a rarity;
allow the overall project (from first thought to eventual obsolescence) to generate enough revenue to pay for the injection mold and profits adequate to keep the molder solvent and eager to take on the next job.

Who'd be a mold maker?