Why won't they move past the issue? It won't win them any supporters.
Many believe in a vindictive God Who treats any offense to His Authority with eternal damnation. To avoid such damnation people must suffer greatly in This World so that they can avoid ending up in Hell for sins. To them, abortion is murder. (As a side, evolution is either blasphemy or heresy deserving an eternal stay among the worst of all souls).
The link between belief in a God Who acts more like a gangster or a fascist tyrant than like a good and decent person and right-wing politics should be obvious. Hard Right politics has submission to authorities beyond question as a cornerstone. Take away the fear, and the whole basis for Hard Right politics disintegrates.