That's because neither party want anything to change. Abortion solidifies both bases and nothing actually needs to get done.
I'm personally against abortion. However, my view has changed over time to realize, this isn't a governmental issue. It's a societal issue. If people want abortion rates to drop more, they need to do what is needed in society so women don't feel the need to get one. To some people, that's abstinence. To others, that's adoption. For yet others that's realizing they have support systems so they can have the baby and support it themselves.
We will never get rid of abortion 100% even if we make it illegal. So, why not concentrate on caring about the people involved in the issue instead of demonizing them?