I feel like your initial question can be applied to a lot of things. For instance, Elher Danlos Syndrome has 13 variations depending on which gene is mutated. This include 11 known mutations and 2 catch-all categories for variations where we haven't yet found the mutation. Why are all these mutations under the same disease when they have such a range of symptoms? My guess is that it is because they were all lumped together before we had the language to talk about them as separate things or the technology to identify the causes. Going back and saying oh all these people don't have ASD or EDS or whatever but this specific thing that we have now identified might cause some disruption is research and awareness.