For them, abortion is extinguishing a life. In this case, the fetus, although no longer viable due to mechanical impossibility BUT still connected to the umbilical cord and inside the placenta, gave it a heartbeat. Any human intervention that would cause that heartbeat to go away, such as inducing labor, manual or physical extraction, or even manual dilation of the cervix, since the fetus being way too young to survive outside of the mother, would end up being the cause of that heartbeat going away, and thus, murder, in their eyes. All they "can" do is "Let nature run its course"
It is beyond stupid, cruel and horrible. Those laws are actively killing people through neglect.
Edit: Miscarriage does not mean the fetus "died", it merely means failure to carry to term or to point where the fetus can survive outside of the mother, which is usually flagged at 20 weeks. When labour started, at an unsustainable pregnancy length, it is counted as a miscarriage because the fetus can't survive on it's own, however it was not a spontaneous abortion because there was still a heartbeat.
You clearly underestimate us, you sexy thing