Gardeners care about their direct relationship with soil, plants, and food. To grow plants from seed bought from others is one level of relationship. To save seed to grow new plants goes to a deeper level. Saving seeds of squash and pumpkin is unusually easy. The flowers are big, dramatic, and easy to handle.
Hand pollination is fast and simple.
C. moschata includes 'Tahitian Melon Squash', 'White Rind Sugar', and all the butternut types. Incidentally, there's little rhyme or reason why a cucurbit variety is called a squash, a pumpkin, or a vegetable marrow. For example, you can legitimately call any squash a pumpkin, and vice versa. When looking for a specific variety in a seed catalog, however, look under both squash and pumpkin. Squashes and pumpkins are monoecious, meaning each plant has separate male and female flowers.