Glow Squid do not spawn in Superflat

Glow Squid cannot spawn in Superflat where the conditions for their spawning are otherwise met. Recreating the same environment which spawns glow squid in a regular world in Superflat will not spawn glow squid.

I am not aware of the technical details behind this, so I am hopeful that someone more knowledgeable will be able to provide more information off the back of this post.