I'm sure you'd find a great number of those Democrats on the pro-life side of the fence are Christians. Those who believe that life begins at the moment of conception etc etc.
But for the first time in many years (in 2015) the number of Americans identifying themselves as pro-choice surpassed those who identify with pro-life - by 6% (50 - 44).
We hear more of the pro-life - or anti-abortion - side because they're far more vocal.
Not all are vocal, but I think that in part reflects that the conversation was lost ages ago. Of all the political issues of the day, this seems to be the one that remains from a prior generation. I won't argue the merits of pro-life vs pro-choice here, but there are more than a handful of considerations that I'm not aware get discussed on this issue, including the rights of fathers and the rights of children.
Interesting about the number above--44% of Americans are pro-life. If that's a good number, then far more Americans are pro-life than pro-Trump. While you and I might marginalize the Trump supporter, clearly this group is not insignificant in number.