Can you be even more simplistic? You talk like they are just shooting craps, smoking and joking. That's not all they do.
A main trick in our political systems is to talk about who voted for what. Cool. Easy for the popular press and easy on the mind of the civilians. But, that's nothing and so the press and the politicians agree, it's a fine smoke screen.
I assure that is not the question.
If we don't WHY this person voted one way on one bill and the other way on the next, then we don't know shit about it.
The votes are not for sale, like that is a bad thing. The votes are for sale and that is a good thing. It's how it works.
Yes, there is real money involved. But, it's not so simple. Each vote is priceless. The course cannot be altered without votes.
Each vote is unique and like an N-demensional Chess game, all moves are final. All moves have consequences. And like in Chess, there is a clock.
So, why he voted his party has to do with the price of his vote. The price of his vote is party support for re-election.
No, it is even more subtle than that. He doesn't want to be put on the Shit Panel of the Shit Sub-Commitee working on Excreta removal.