Because of the ick factor of implantation? Or the concept of surrendering bodily agency?
I remember when I was young a friend broke their leg badly and needed one of those devices with the scaffold that has pins going into their legs, I couldn’t even look at it it freaked me out too much. Maybe that experience gave me a phobia
and i had bad ankle break a year or so ago, and needed lots of external meccano to stabilise it. it wasn't fun, and very inconvenient, but not too painful or scary.