Sarah Longwell made a point on a podcast recently that while abortion isn't always listed as a top issue for voters in surveys, at least in the focus group setting, when you peel back the layers of the onion a bit, people end up displaying a lot of passion and intensity around it.
I suspect that's a little of what's at play here.... when the rubber meets the road and when people step into the ballot box, it's something that manfiests.