I agree that polling on this issue is very complicated.
The arguments are in the extremes, but most people are in the middle. In general, about 30% of Democrats want no restrictions on abortions, and about 30% of Republicans of want abortions to be illegal.
This is from 2019, but the numbers seem to be fairly consistent over the last few decades.
That leaves a whole bunch of people that want abortion legal, but with restrictions. Most are not extreme on this complicated issue. Nobody wants abortions to have to happen.
So, the issue always comes down to what are "reasonable restrictions". There's obviously where most of the debate is.
Why there are more restrictions now? That's a great question. I doubt it has much to do with public sentiment fundamentally shifting (though, I'm open be wrong on that if there's some evidence).
I think a lot of it is people just not paying attention. Most don't pay attention to state politics. Similar to how rampant gerrymandering can go on without people raising a stink. And there's a whole bunch of people that just have no reason to care or pay attention to abortion access/restrictions.
Many are just going about their lives not really paying attention because it doesn't affect them. They figure, it's legal, so it must be fairly accessible (having no idea how wrong they are). I've been guilty of this most of my life.
So, the policy ends up being written for the extremists on the issue.