A lot of pro-lifers became pro-life after getting an abortion, seeing that it was a baby they killed (not just a "clump of cells"), and then naturally deeply regretting it. Other times, people are lied to or confused. Doctors are happy to dehumanize babies with their language if that's what the woman wants, and some abortion techniques are also used to remove the bodies of babies who die naturally, so people think they are getting an abortion when they really aren't.
Most abortions are by pill, but that doesn't mean there aren't techniques for every stage. All the information I gave you is freely available online with a quick Google search. And not just from pro-life sources, but pro-abortion sources as well