You didn't ask for the foundation at first. I don't believe I'm avoiding and answered the question already. Your skier example essentially asks the same question.
Here is your descriptive answer:
Unless a doctor is willing to risk going to prison, they will abide by law. So many don't perform abortions in states where it's illegal or hand out abortion medication within the state. This is your descriptive answer as to why abortion is currently the exception in descriptive terms.
Here is your normative answer:
In other words, your question has a false presupposition. Abortion is not the safest medical procedure as the act of abortion causes great harm to others. Abortion ought to not be considered the safest medical procedure to all impacted parties in the vast majority of the cases (except when mother's health is at grave risk such as over 50%+ chance of death).
As for foundation, the foundation is moral reasoning. Acts of commission that causes harm to others is wrong.
Your conflating legality with morality. Many states also support the right to be dishonest to family members, lying in relationships, refusing to help people in dire need, and treating people badly. Just because one has a legal right to commit an act does not mean that it's moral. I say that it's morally wrong.
Then the laws ought to be changed to remove any loopholes because abortion causes great harm to others.
You didn't because you conflated legal concepts with moral arguments.