Because nobody really cares whether it's technically cyberpunk, steampunk, clockpunk, or weirdpunk, these all very clearly fall under one particular umbrella.
"The Justice League of Victorian England." So, steampunk?
Dieselpunk? It has walking carnivorous cities, it's definitely in this section **somewhere**.
China Mieville-punk. This book truly defies genre boundaries, and ranks as one of CUSFS' all-time favourites. Just go read it already.