In Britain (excl Northern Ireland) a country close in many respects to the US - in terms of religious history, society, status of women, medical ethics etc abortion is rarely a political issue.
The Act of 1967 made it virtually available on demand up to 28 weeks. This was reduced in 1990 by the Human Fertilisation and Embryology Act to 24 weeks, and allowed on the following very wide and encompassing grounds, certified by two doctors:
Ground A – risk to the life of the pregnant woman; Ground B – to prevent grave permanent injury to the physical or mental health of the pregnant woman; Ground C – risk of injury to the physical or mental health of the pregnant woman (up to 24 weeks in the pregnancy); Ground D – risk of injury to the physical or mental health of any existing children of the family of the pregnant woman (up to 24 weeks in the pregnancy); Ground E – substantial risk that if the child were born it would suffer from such physical or mental abnormalities as to be seriously handicapped; Ground F – to save the life of the pregnant woman; or Ground G – to prevent grave permanent injury to the physical or mental health of the pregnant woman in an emergency. (Wikipedia)
It has never been a party-political matter, rarely gets into the headlines - except when Northern Ireland is the subject of discussion - and most people, other than a few activists, seem to accept the law as it stands as reasonable.
The political position in the United States could not be more different. There it can decide elections, even the presidency - and it is the key issue determining appointments to the supreme court. It plays a huge part in dividing the population, and individual states, into two rival camps.
A gulf also separates the US from the UK on the matter of gun control - but there the reason is more obvious, given America's history as a frontier society. But quite why the US is so divided on a matter which can intimately affect any family, where it hardly ever enters a panel discussion, let alone an argument in a pub in Britain, is puzzling.
An article in this week's edition of The Economist entitled What happens after Roe? suggests the following:
In other countries abortion tends to be embedded in broader health-care systems. In the United States it is practised almost exclusively in stand-alone clinics, largely so that providers can avoid the costly billing systems found in hospitals. Yet this has made the job of anti-abortion campaigners easier, allowing them to find the right women to shout at and enabling them to portray abortion as being separate and different.
Somehow, it seems to me that this cannot provide the whole answer - there has to be a more basic reason.