It's something I've covered here and there before, but as occasionally happens, I wrote an entire blog post in someone else's comment section. Here is the post, about some nude model with already large breasts who's gotten them enlarged several times nevertheless. Not too different from the "sweater girl" phenomenon of the mid-century, exaggerating their chest size with bullet bras in order to prop up their sense of self-worth.
When people cocoon, they lack the feedback from others that tells them where they rank -- pretty, average, ugly, etc. So they take up solitary pursuits like breast augmentation to convince themselves that they're worthy -- y'know, rather than putting themselves out there for the boys and seeing how many date offers they get.
Add body dysmorphia to the list cocooning's web of dysfunction.