The distinction between eons is based on very broad planetary developments, like the formation of an oxygenated atmosphere or the emergence of multicellular life. For example, the Phanerozoic eon reflects all time in earth's history since the appearance of shells in the fossil record. Other subdivisions of the geologic time scale (including eras, periods, and eons) require more specific observations based on the existence of specific species or geochemical conditions. Why do you think there are no subdivisions for the Hadean, Archean, or Proterozoic eons?

Answer

The Hadean time is about 4.6 to 4 billion years ago . No rocks of this time is found on the Earth excluding some meteorites.

Solid rock formed on the Earth is most likely happened prior to 3.8 billion year ago, but strong evidence for this is still not available.it is quite possible that Erosion and plate tectonics had probably destroyed completely all of the solid rocks that were older than 3.8 billion years ago.

Archean Eon is round which lies Between four billion and two and half billion years ago, the continental protect rock started out to shape. Approximately 70 percentage of continental landmass changed into shaped in the course of this time. The Earth's continents began out to shape withinside the Archean, even though information about their formation are nevertheless being debated, because of loss of considerable geological evidence.

By the Proterozoic eon, lithospheric plates had shaped and began out transferring consistent with plate tectonic motions just like today. As those plates shaped and began out transferring, ultimately a supercontinent shaped from collisions as the sea basins closed. The specific variety of supercontinents in the course of the Proterozoic (or earlier) is still unknown.
These are some point that there is no sub division for these eons.