Why is there no highest level in the iterative hierarchy of sets?

In the iterative hierarchy of sets, there is no highest level because the construction process is inherently open-ended and recursive.

At any given level of the hierarchy, one can always construct a new, larger set by taking the union of all sets formed up to that point and then applying the power set operation to those elements. This process can be extended to arbitrarily high transfinite levels, indexed by ordinal numbers. Because there is no "last" ordinal number, the iteration of these operations—forming unions and power sets—never terminates. Consequently, for every set $A_{\alpha }$ created at a specific stage, a subsequent stage $A_{\alpha +1}$ can always be generated, ensuring the hierarchy continues indefinitely.1