I believe it's more the rampant insider trading that illustrates their selfishness.

Trading with non public information

I think that's a bit of a strawman.

If everything has a price, the potential to receive that price without much risk encourages your selfishness. Owning stock while being able to make policies that can immediately affect that stock incentivizes selfishness.

Politicians are not suppose to be in the game of maximizing their personal profits.

Owning stock is not, but buying stock based on private information is insider trading. Engaging in insider trading is most definitely selfish, and technically illegal.