It’s the two party system. The choices you’re given are what the largest groups in each party are in favor of, not what most people prefer.

So with Republicans, most Republicans are pro-forced birth, so that’s their platform, however unpopular it might be.

With Democrats, you don’t notice it as much because the largest bloc in the Democrats is basically the “Centrist” group. But that’s also why they keep doing these bone-headed “Trying to be Bipartisan” things that nobody except columns for the New York Times really likes rather than actually using solutions that work.