Yeah, there probably aren’t many good reasons to actually make a Gnome Ceremorph, but it does get around the problem that would otherwise prevent gnomes from being player characters.
Plus, as it has been mentioned, these tadpoles have been altered for a purpose.
The Illithids seem to be working with the Dead Three to create advanced psionic soldiers using tadpoles corrupted with Shadow magic, so actually creating new Mind Flayers might not be the objective.
