There is a lot of debris in this universe and we are really a long way from sampling such systems let alone classifying them. If anything can be suggested it is that empty spaces appear to have coalesced to form planets or more likely, planets have formed stable orbits leading to all debris been swept out of the way. Again we are along way from knowing.
Seeing the Kuiper Belt as an unformed Gas Giant is instructive. Seeing Gas Giants other than Jupiter as Earth like objects that swept up their share of the Kuiper Belt is also instructive as well and conforms to my Jupiter Genesis conjecture.