Bioadaptive shells were initially easiest to justify in the harshest radiation environments. That justification is no longer the whole story.
Some lineages are now using these layers for reasons that have less to do with survival and more to do with repair buffering, environmental smoothing, and long-route endurance. Once biology proved it could serve as a disciplined support layer rather than only an emergency accommodation, the design logic widened quickly.
This does not mean every branch is becoming bioadaptive. It means the category has moved from rare exception toward normal systems choice in places where ordinary machine architectures alone remain too brittle.