Pro-life leaders tend to treat the pro-life issue as a kind of prolonged hostage negotiation with women: we better do X, Y and Z, or else the negotiations will fail and the kid's going to get killed.
No stigma against women getting knocked up out of wedlock, or she'll ice the kid to cover it up!
No stigma against single mothers, or she'll kill the kid to avoid becoming one!
No treating women who get abortions as monsters, or we'll drive them out of the church - and then they'll probably keep getting them!
So, the pro-life movement has systematically done everything it can to remove all criticism of women who get knocked up out of wedlock, or really, under any situation whatsoever. At the same time, they've struggled to remove all stigma from any women who've had or are considering abortions, in the hopes that they can be appealed to.
And then some of them seem perplexed and disheartened at how we've gotten to a situation culturally where single motherhood is the new normal and women's 'reproductive choices' are sacrosanct, whatever they may be.
There's more facets to this problem, more reasons it's turned out this way. But the fact is that if you want to know why, decades on, the pro-life movement has at best managed a quasi-stalemate, it's largely due to self-inflicted damage. It was a mistake to treat abortion as a numbers game where the biggest goal was in raw reduction in the projected numbers of abortions, instead of as the cultural fight it really was, and will always be.