Purpose of 'bore' on spoke nipples - why are spoke nipples not threaded through their entire length?
Adding threads to any sort of bolt under tension doesn't actually make it much stronger, beyond the first ≈5 threads. Adding more basically just adds dead mass; either way the whole thing will generally fail somewhere close to the first thread. So, filling the bore with threads wouldn't have any benefit. What it would do however is move the expected point of failure out of the relative safety of the unthreaded bore, which particularly protects the spoke from being bent at that point, which would further diminish its strength. The bore makes it so that if there's some bending, it will be on the unthreaded part of the spoke, which is stronger to begin with, so not as worrisome.