Because abortion and being anti-health care is popular with a very, very, very select sliver of people that tend to vote Republican. Most Americans, even Republican leaning voters, are fine with Planned Parenthood. One bit of a credit I will give Trump is that he was perceptive enough to understand that even the Republican base, let alone the general American voter, are fine with abortions being available and gay people marrying. That's just one (of many) reasons he embarrassed the so called finest (lol) that the Republican Party could muster.