Remember when Roe v. Wade made abortion legal, and everything was fine for a few decades... Why all of a sudden abortion is suddenly illegal again? What's going on?

In 1995, 1/4 of Americans started to lose their minds because TV had girls kissing girls, black people, and Mexicans. 6 years later, something bad happened, another 8% of Americans lost their minds, and turned to White Prosperity Jesus, conspiracy theories, and ultra nationalism to salve their weary souls.

Then a black guy got elected president. This, combined with 20 years or growing income inequality drove another 8-10% berserk.

In response, they found the closest thing they could find to White Prosperity Jesus, Creepy Orange Prosperity Uncle, and banded behind him, in a quivering hope that he'd send all the funny looking colored and gay people someplace far away like Mexico, the capital of Africa or something, so that good uneducated people who work 20 hours a week could afford a 4-bedroom house and a Camaro, like it was when their grandpa was growing up.

The party that wants to take away freedoms has more power right now and that's how they exercised it because it's the most important issue to many of them.

It was never fine. There have been anti-abortionists demonstrating outside Planned Parenthood offices for decades. Planned Parenthood personnel have been harassed, assaulted, and murdered for decades. What changed was that the right, seeking a way to desperately maintain any relevance in a quickly liberalising political environment made deals to fight for the same people who we'd've labelled terrorists and criminals. At this same time a dumb ass named Bill Clinton removed the regulations that kept corporations from owning huge swathes of television stations. In addition, Murdoch started Fox News which was born with the only reason to be a propaganda arm of the conservatives. Oh, and then there was the rise of the radio talk show propagandists like Rush Limbaugh, may he suffer eternally in hell. All these worked together to push a more and more extremist conservatism on the masses. They made it seem okay to be hateful and spiteful and mean. They pushed the idea that intelligent people could not be trusted(unless they were conservative and they towed the conservative line). They pushed the idea that empathy was a weakness and that the only person you should care about was yourself.

It didn't suddenly change, it has always been like this. The problem is the masses on the left tend towards being self absorbed dumbasses blind to what was going on around them - especially the white ones. The white ones thought everything was just fine and dandy because it was for them and they had that one black friend so they totally weren't a racist. And racism was dead because of that, too. The Democrat Party has, for decades, been a disjointed mess led by people who are only vaguely competent to lead a room of kindergartners. There is one saying I've known for decades - "The Democratic Party is the only one who can snatch defeat from the jaws of victory." In addition, hubris on the part of Ruth Bader Ginsberg kept her from retiring when Obama had a majority of Democrats in the Senate. So instead she wound up giving her seat to Trump to fill.

There are so many more things I could list, but won't because I don't want to spend all night going over what you'd get in a polisci course about the last 50 years of American politics. There is, however, one last thing I'll touch on - that every time the Democrats have had a control of the Presidency and Congress, or even a veto proof majority, they never, ever took the time to legalize abortion. Consider that for a moment. This whole mess could have been avoided had the Democrats had the fortitude to do the right thing. They never did. They played just as much a game with women's bodily autonomy as the GOP did. There's no side that is innocent in this mess. I am not "both sides"-ing here. They're both responsible for it in different ways - the Democrats because they valued their seats more than women's autonomy and wrongly banked on RvW always being there and the Republicans who actively sought(and still seek in many states) to destroy women's bodily autonomy not because they believe in it, but because it gets them votes.

I wouldn't say that things have been fine for the last few decades. From the moment Roe was passed anti-abortion advocates made it their mission to either limit its impact or have it overturned. Usually this was done through protesting abortion clinics or having state legislatures with Republican majorities write laws that went right up to the edge of banning abortion. Even before Roe was overturned you had some Republican states that only had one clinic that was able to provide abortions and Republicans were always looking for ways to try and shut them down. However, the most effective strategy has been making sure the federal courts are packed with judges who would rule against abortion providers. It mostly flies under the radar, but nominating judges and having them confirmed by Congress is one of the more important things a President can do because those judges will stay on the bench for decades. For example Trump made 226 appointments in just four years.

And that brings us to why Roe was overturned. Because for the last few decades, but especially during the Trump years, conservatives made it their mission to have a Supreme Court with a conservative majority that would overturn Roe. Of course every SC candidate nominated by a Republican had to say that Roe had decided the question of abortion, but it was open secret that the candidates Republicans nominated would, hypothetically of course, overturn Roe if abortion came before the Supreme Court. During the Trump years, conservatives finally got that majority. Due to a series of deaths and retirements in the Supreme Court conservatives were able to finally have six conservative judges vs. three "liberal" judges, a balance that is going to be in place for decades thanks to the way the Supreme Court works.

Abortion has never been "fine" and has been debated furiously worldwide since the age of time. For a very long time the US was a world leader in abortion laws if that tells you anything about how debated it is worldwide.

If you are able, the BBC did a very good radio programme on this as part of its ‘Things Fell Apart’ Series - The story behind the beginning of the abortion culture war

Let me reference a comprehensive post on the matter from reddit's r/askHistorians. It's worth trying to understand your society at a deeper level than a five year old. This supports mutual understanding and, as a consequence, the effectiveness of democracy :).

Edit: Removed the copy-paste from reddit. This is ELI5 after all.