Trump said he could shoot someone in Times Square and his base would still support him. You can't reason with them, it's not about facts, it's about prejudice.
It's because he's pro-life and supports Christians. You could be the worst person in the world, but if you claim Christianity and choose pro-life, people will not reject you in favor of someone who is for abortion rights. Why? Because people who find abortion unconscionable cannot sacrifice their will to protect the unborn in order to expediate some other goal.
Now if there was a Democrat who was truly pro-life who ran against Trump, it might be harder for some voters to support him, but many people simply won't trust a democrat not to flip-flop on their stances because Democrats are usually party conformists who will fall in line with their party, one way or another. So I wouldn't expect a Democrat who claimed to be pro-life to actually stick to her or his guns once in office. More likely, I would expect some pragmatic compromise to happen as quid pro quo for funding some other program, etc.