How come new planets don get cool names anymore?
Sure they do! It’s just that we haven’t found new planets in our solar system, but astronomers give distant planets that were recently discovered good names sometimes. Other times they just classify them by numbers until they can think of a good name. There’s Persephone (once suggested for a new planet), Eris and its moon Dysonia, which are planetoids in the Kuiper Belt beyond Neptune. In that same belt there’s Makemake, Haumea and Pluto, all dwarf planets. Sedna is the most far away object inside the Solar System, recently discovered. It’s still not clear whether it’s a planet, but it could be, since it has a satellite of its own. Some minor planets in other solar systems have neat names. Take these for instance: Athreya Audubon Aventini Baillauda Balam Cannat Casals Messier Sagan etc. Here’s a really long list of names for planets, planetoids, and other objects from Harvard U: http://www.cfa.harvard.
