Walking dead and spectral dead intellect

An oddity I noticed in the distribution of undead intelligence scores is that the incorporeal undead are almost always of average intelligence. Of those in the MM, only the shadow has INT lower than 10.

I don’t understand why this would be the case. In general I would have expected the specter, will-o’-wisp, and wraith to have lower intelligence. I would’ve expected at least some spectral dead with comparable intelligence to zombies and skeletons.

Or perhaps, more likely, the writers didn’t give much thought to what effect intelligence had on the fluff. 

In real life, the voodoo religion tells of “astral zombies” as the spectral counterparts of regular zombies. These spirits are enslaved by bokors and used to perform various tasks.

In a future post, I plan on dedicating thought to a more thoughtful ecology of the spectral dead. With influence from The Lord of the Rings too.