Why does the Republican Party pretend to be "pro-life"?

People fall for this all the time. In 1973, when Republican president Richard M. Nixon was in office, three out of four of his Supreme Court nominees voted in favour of Roe v. Wade. Then we had the Republican Gerald R. Ford who gave us pro-choice justice Stevenson. Then we had Republican Reagan who gave us Sandra Day O'Connor. Then we had George H.W. Bush, who gave us David Souter. Eisenhower also gave us justices who voted in favor of Roe v. Wade (although to be fair, there was probably no litmus test way back then regarding what was considered socially unacceptable). So, why do people who are pro-life support the Republicans when so many of their presidents have given us pro-choice justices. Could it be that these Republicans know that if Roe v. Wade were actually overturned, they could lose a lot of their one-issue voters?