system
Given the following post, respond as if you're commenting on Reddit:
human
[Jimmy Neutron] The Yolkians are completely helpess without their suits. How could they have gotten so advanced with no hands, legs, or anything but a slug-like body?

Their suits are specifically designed to hold their phlegm-y bodies, so I doubt the suits came first and they eventually evolved into Yolk.  At the same time, their entire culture, even their names, are based on their egg-like appearance, so it must have been like that for quite a while.

They worship Chickens as gods, which could explain their egg-focused culture, but the Chicken used in their ceremonies is unintelligent and brutish, I can't see one of THOSE being the source of their robotic bodies either.
gpt
They're like the inhabitants of The Axiom in Wall-E: technology became such a part of their lives that their bodies began to devolve into a more primitive state, and as it occurred they built incrementally more advanced machines for themselves, until they eventually arrived at the state you see them in now. They've been that way for so long that they've lost all memory of what their previous bodies were like.