A computer is much more likely than your body to have small, self contained parts that just function. Your body is the result of millions of years of accidental evolution - See the canonical example of the laryngeal nerve in a giraffe. Computer programs are often designed to be small and modular. They might have to worry about memory layout shifting because some other program grew - That's nothing like your spleen trying to occupy the same physical space as your stomach and causing digestion issues.

For all of medical science's experience and history with debugging the human body, there's still so much more to understand.