For some of us, if I find a kit at a good price it is convenient to get all the little parts like engine blocks, centering rings, engine hook, parachute, etc. For other people they have boxes of those things so they can probably pull out the parts that they need, cut some fins, and get with the assembly.
I was going to buy a Goblin kit but build it with different fins, so if I could find the nose cone I could just build from other parts I already have. As far as I can tell the plastic nose cone used in the Goblin is not available for sale separately.