Well because miniature moulds are made of RTV silicone (some might need vulcanizing but that's beyond my narrow knowledge) they can have undercuts, which the machined steel moulds for injection moulding can't have. That's why plastics have those odd flat spots where the detail just sucks. A spin caster for metal casting is a relatively (small and ?) cheap item compared to an injection moulding rig.
The strength of the green, master, RTV mould and spin caster is relatively low start-up costs and very low costs for new figures once you're set up. I can't say what sculpting costs, especially now properly applied CAD can do perfectly good sculpts (that then need to be 3D printed and touched up before being mastered at extra expense IIRC.... but reposing and changing weaponry on an established sculpture takes minutes) but moulds cost a couple of hundred back when I was researching this stuff around 2002AD, maybe.
So, working in metal you might get a new miniature into production for a few hundred dollars where the machining for injection moulds would be 1000s or 10,000s, IIRC, bobloblah would know better (is injection mold the right term, even?). That might mean that the regular release cycle is not only good for your image, it might be your "comparative advantage" over plastics as well, I wouldn't know, but it sounds like it makes sense, right?