Asset crunching time

I've been running a live Unity game for the past few years which is on 5 platforms. While I keep a different folder for each platform so I don't usually have to worry about platform switching, occasionally things happen that require me to upgrade Unity (in this example it's the 64 bit requirement for Android builds). Whenever this happens of course, I spend a godawful time in crunching assets mode, especially since this particular upgrade has had me go through numerous versions of unity trying to find the one that both supports Android 64 and doesn't have game-breaking bugs (I'm still working on it after two weeks...)

I decided to build a new custom 12 core AMD 3900x rig to help speed up this type of stuff, and noticed I'm really not seeing much of an improvement at all. Why isn't asset crunching using all available horsepower? It seems like a process that could be easily multi-threaded.