At which point here the dependent is using the other person's body? I mean literal blood, marrow or organs... In your scenario, someone can literally pay other person to care of the dependant. It doesn't involve the same rights or circunstances.

Because the fact is that a phoetus is using and altering the woman's body to develop. Literal. And the woman's live might be at risk. Giving birth is painful and has a difficult recovery. Sometimes live lasting consequences. Interestingly enough, you ignore this again.