I think they skip Numbers because it contains the only story in the Bible that mentions abortion.
Brian Amberg

It was just a bunch of cells that nobody, including God himself, cared about.

It does look weird, looking back with hindsight. So great was the rigor of the Levitical law, that martial fidelity trumped the life of unborn infants. Christianity must have brought about a greater concern for the individual; ancient Israel was a very collectivist society. It’s unsurprising that people who support eugenical choice with regards to (say) autistic people, are generally collectivists.