Because you start from only one embryo. Almost all animals start from one embryo. These animals are formed from thousands to millions of embryos. From a feat

Because you start from only one embryo. Almost all animals start from one embryo. These animals are formed from thousands to millions of embryos. From a feature categorization perspective, I guess you have a point. They look a lot like non-clonal jellyfish in practice! But the implied underlying question is: how did that mechanism evolve? Two organisms may look similar but have completely different evolutionary histories and mechanisms to arrive at that appearance. Like eyes, which seem to have evolved independently multiple times. This is a completely different mechanism to construct a multicellular organism. Not stem cells, but embryos, cloning a specialized twin, each of which undergoes embryonic development into a sort-of-organ. In almost all other animals, all genetically identical specialized cells come from a single embryo, which splits into stem cells, which then specialize. That's why it's interesting and stands out, at least to me.