They aren’t from aborted babies. Stem cells. “In the 3— to 5-day-old embryo, called a blastocyst, the inner cells give rise to the entire body of the organism, including all of the many specialized cell types and organs such as the heart, lungs, skin, sperm, eggs and other tissues.”
And, in fact, they used “left over” embryos that were created for reproductive purposes, with the donor’s consent.
A 3 to 5 day old blastocyst hardly constitutes an abortion. After 5 days the embryo is useless for stem cell harvesting.
I remember reading something about getting stem cells from an umbilical cord, but I don’t think an abortion would be required for that.