Plastic cups, dishware, and toys are most commonly made using the process of injection molding because they are common consumer items that need to be produced on a mass scale, and injection molding (once the hard tool has been created) is designed for mass production.
Master patterns for cast urethanes can be created with CNC machining (which is a common process for injection molding) but cast urethane master patterns are often created with additive manufacturing (or 3D Printing) and the reasons for this vary.
The care that goes into a hard tool involves intense machine programming which costs thousands of dollars alone.
Cast urethane master patterns can be produced using machining, additive manufacturing—even an already existing product.
Cast thermoset urethanes have better physical properties than most injection or extruded thermoplastics.