I don't think they need to. For the most part, it's just convenient for the majority to not get anything done and it's campaign material for Manchin to betray the party. I think that by and large, it's a symbiotic relationship where both sides get what they want.

There doesn't have to be a conspiracy for this behavior to occur organically. Both parties represent different factions of the bourgeoisie, and different factions want different things but are united in interests common to being bourgeoisie.

I think it does happen once in a blue moon. Congress is more educated on their votes than the general public, and sometimes all the information isn't public. Once in a while they feel they're going to need to make a vote that isn't popular with their base, and might actually do the rotating villain thing. But that's also going to take into account how strong/weak they are in their districts, and would never be Manchin or Sinema.

We might even see this more in the near future, where Congress is being briefed by experts, the military, the FBI, and the CIA while the general public is being briefed by AI-powered social media propaganda campaigns.

Of course people like to blame the "rotating villain" every single time the party does something they disagree with, because obviously the user's opinion must be the majority opinion.

You really think no back room deals ever take place in congress?