Why are all the politicians corrupt,greedy, selfish a- holes??

The system does it to them. You can go in with the best intentions, but you'll soon find that without political and financial allies, you can't get anything done, and probably can't get reelected either. So you either make political and financial allies, by doing something for them, or you fail.

Because they would be unsuccessful politicians if they weren't

from all my accumulative experience of politicians i'm more convinced than ever that politicians should be done the same way as jury selection is done.
Everybody gets a go, you're selected randomly, and when your time is up you go straight to the back of the queue before you get the chance to go again.

To think that you deserve to be in charge of a whole country of people takes a good bit of assholery in itself... so it's no surprise that all the people going for that job are assholes 😒

1. I don't think this applies to all politicians. 2. To the extent there are, in the end the blame lies with the public. Flash over substance often prevails.

Who else would Want to be a leader?