Polls show a majority of the country was against Roe and Casey being overturned.Only 34% of Americans (give or take) believe that abortion should occur in the second trimester. Even less believe they should occur in the third. Why would anyone who is mostly anti-abortion negotiate an additional 5 to 8 weeks (or more) away from their position when a solid 2/3's of the country do not support that?
The public at large has already arrived at the current compromise between the two extremes and that compromise draws the line in and around the first trimester.
Why not just draw a line down the middle and be done with it? Both sides get half of what they want.