I have been studying the Iterative Set Concept within the context of the paper titled "Modal Set Theory" from Menzel specifically on pages 11-12.
"As we’ve just seen, the iterative conception of set provides a cogent answer to that question: only those pluralities that “run out” by some level of the cumulative hierarchy constitute sets at the next level and, obviously, the entire hierarchy is not such a plurality; there is no level at which the members of all the levels form a set. Rather, the question is: Why is the hierarchy only as “high” as it is? Why do all the urelements and sets that there actually are fail to constitute a further level that kicks off yet another series of iterations?
I understand that in this context, the question pertains to why a particular set is at its level within the hierarchy and why existing sets do not seem to initiate further iterations. I interpreted the former as being naturally determined by the definition of sets, so I'm unsure why this question poses an issue. As for the latter, I couldn't grasp its significance. Why is this question problematic within the framework of the Iterative Set Concept and the hierarchy of sets?