This may be wrong or apocryphal or a third thing:

But I recall reading that this is a deliberate affect used by those who work with nuclear material. Partly as a shibboleth, partly as a means of making the word easier to say quickly.

It came up because George W Bush would pronounce it “nucular” and that was given as the reason. All if my memory serves that is.

It would make sense as a different spelling and pronunciation I guess. Like "molecular" or "ocular" or "particular". Fits in better.