Not as many American’s are ‘pro-life’ once they realise what that actually entails. People seem to think that ‘pro-choice’ means you’re in favour of a free for all approach to abortion; the reality is more nuanced than that. People who are pro choice still favour restrictions but want the choice to be there. That is the key.
Many self-described pro-choicers favor some restrictions on abortion, but it is certainly not the case with the abortion lobby or most pro-choice politicians. Favoring any restriction on abortion is enough to have you labelled anti-choice and accused of waging a war on women. So long as Roe is in effect, that's where the policy debate is.