IMHO, it's just because the Republicans are better at playing the game. So rather than saying there can be no abortions at all, they'll just keep narrowing the terms until the margin is so narrow as to be insignificant. You can have an abortion if you've been raped, for now. Oh, but only if you don't use public money. And it's been a certain kind of rape. On a Tuesday. If you're a Libra.
They've given up on an outright assault and resigned themselves to a war of attrition. I don't believe it's an idealogical concession they've made, just a superficial, temporary, tactical one.