I don’t want abortion, either, but it’s been unsuccessfully challenged so often and been in place so long that it is considered ‘settled law’.
Despite that, there is a far more concerted effort to remove abortion than to remove same sex marriage. To be fair, same sex marriage has only been judicially imposed for about a year and a half now, so one wouldn’t expect that the opposition would gain their balance and begin a counter-offensive.
It’s one of those issues of sapping the demand.