Because it hails from a time somewhere between the Iron Age and the Medieval.
I don’t think Classical Romans really cared about abortion or at most, when it was disallowed, it was for “Romanian” reasons.
They largely went by Aristotle's beliefs that the embryo progressively gained souls and finally gained the "human" soul at the quickening (when the first kick is felt, which is normally 18-20 weeks), a belief that would continue to be held by medieval types (Aquinas and St Augustine etc); this meant abortions in that time were divided into pre- quickening procedures (sometimes a necessary evil) and post-quickening abortions (homicidal). Ironically it was the modern scientific understanding of embryology that really codified the modern anti-abortion movement (which is not to remotely imply that the pro life movement is scientifically literate as a whole - this bill being a good example with its talk of embryos being "living infants") - it swept aside all the old ideas of souls being magically injected and granting life in favour of the modern understanding that the embryo is always human.