ELI5

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.