> Some (almost completely openly) accept actual bribes.

This is explicitly illegal. If you can actually prove this you can prosecute them for it. If you can't actually prove it, it's just speculation and innuendo.

> The cost/friction of passing new laws or amendments is still usually quite high and even if you have a majority in both houses and the president there is only so much you can achieve in 2-4 years.

When the parties want something the other one doesn't, they write the text when they decide they want it and then put it on the stack of things to pass the next time they're in power. Half of these things don't even get debated, they just get tacked onto the Patriot Act or Inflation Reduction Act or whatever this year's odious omnibus is for the party gets to ram through the things they want.

It's a stupid way to do things, but it's still what happens.

> Then even these days both parties are not 100% monolithic and there still might be some splits across party lines on less publicly visible issues (the members of your party who are on the fence might start demanding stuff in return etc.)

That just means that even your own party doesn't agree they want it, which is exactly the sort of thing you don't want to pass unilaterally -- it's a minority position that can't get 51 votes even when the proponents' party has 55.

> e.g. Roe v. Wade would be brought back immediately after progressives/liberals had a majority

Not necessarily. The problem with Roe v. Wade was always that it was created by activists -- regardless of what you think about it as a matter of policy, the word abortion doesn't appear anywhere in the constitution and the logic of the opinion would constrained the government from interfering with a variety of other personal and healthcare activities, which inconsistently was never applied. People wanted a right to abortion to be in the constitution but it isn't in there and they didn't have the votes to amend it, so they made one up out of thin air. If you want it, the right way to do it is to get the votes.

But the other interesting bit is that the word abortion doesn't appear in the constitution, and the federal government is one of enumerated powers. So there is a much stronger argument that the federal government should have no power to regulate it, i.e. a national abortion ban is arguably unconstitutional because it's beyond the federal government's enumerated powers.

Now you give that case to a Court with a liberal majority, or even one with a few opportunistic liberals and a couple of conservatives who are true to their principles, and you could get something that isn't Roe but is going to shut down the flip flopping by punting it out of federal jurisdiction for the foreseeable future. And if you want to put on your political hat for a second, the Justices have the incentive to do something like that, because they hate politicizing the Court (protesters show up to their houses and threaten to kill them!), so telling everyone "either go bother the state courts or pass the constitutional amendment, we're out of this" could be a sticky equilibrium.

I'm not saying that's going to happen, but it's the sort of thing that could happen and would be a convenient result for the people whose decision it is to make it happen.