At the time of the Roe v. Wade decision, most evangelical Christians didn’t care about abortion. Back then, people who were against abortion were almost exclusively Catholics, while evangelicals are protestants — you know the people whose name comes from the fact that they protested against the Catholics.
But six years later the GOP needed a new issue to rile up the social conservative base, so they got together and invented one. However, it didn’t work at first, so they had to really “force the issue”. After all, abortion isn’t mentioned at all in the bible, so they couldn’t just do what they did with gay rights and twist a few obscure passages to meet their needs. They had to make it up from whole cloth.
And they succeeded. They succeeded so well they actually got people to commit murder in the name of protecting the sanctity of life.