The Democrats did nothing about it while in power, plus Trump has said he'd veto a national abortion ban (for whatever that's worth). Republicans know abortion is a losing issue for them, for example Ohio keeps voting for Trump but has legalized marijuana and voted abortion rights into the state constitution. Most voters have resigned to fighting for it at the state level, it wasn't a presidential issue for them this year. And on other issues, Democrats weren't convincing that they had much to offer.