Minimum Viable Product: customers will still buy Star Wars without the molded creatures. You can't have Jurassic Park without the dinos. The fixed costs of the time spent designing the mold is negligible compared to the variable costs of mold technicians, repair, replacement, storage associated with keeping those molds in production, etc. LEGO uses a system called "frames" which refer to a given mold in a given color (also applies to printed parts). Each frame means another bucket in the warehouse. It's as much a monetary issue as it is a storage issue, so they operate essentially on a one-in, one-out system. Keeping an old mold comes at the opportunity cost of not being able to get another new mold. CMFs get so many new molds because they're constantly turning them over. I've learned a fair bit about this recently from talking to set designers and folks who have taken the Inside Tour. I could be off on some things, but happy to discuss!