Because the navel chakra/Lower Dantien has appeared in some many different magickal experiences that it might as well be considered “real” and also, not linked to enslavement, or maybe I just got the key when I did this working (linked for people who weren’t have back then): The venom of Azi Dahaka (@Asorotiath, that describes the work I did btw)
The solar plexus chakra could be just a function of all the nerves in that area, but that and the heart are useful for healing work, and other acts of (especially) benevolent will and influence on others, who are ill or whatever.
There are also subtle energy centres in the head, and some people open up, or alter, their energy bodies spontaneously over time.