During the 111th Congress, from the appointment of Al Franken until the death of Ted Kennedy, as well as during the term of his appointed successor Paul G. Kirk, the Democratic party held 58 seats in the Senate and caucused together with 2 more senators.
There were conservative democrats such as Manchin and leiberman who beleived their constituents weren't in favor of abortion rights. A straight party line vote on abortion rights wasn't going to happen. There were also republicans in more urban states that knew the majority of their constituents favored abortion, but because they were worried about being primaried they wouldn't vote for abortion rights.
Sure but the possibility of getting dem senators from red states to vote for abortion was extremely, extremely unlikely. Republicans tend to stick together but Democrats do not on these slim "majorities". Check out Manchin and Senema, they are essentially moderate republicans despite their party affiliation. They are heavily sponsored by right wing corps and PACS.