Why are politicans not libertarian?
After about two weeks in office they figure out, that if there is no graft in government, there is no point (for them) in being at the top.
Some rich people run for office and steer contracts to their companies or to their husband's companies (Pelosi). It is rare to find someone honest as Palin, who turned down Fox News contract, resigned from an oil board to be free to reveal the shady dealings going on, and resigned from being governor to avoid killing Alaska with legal dealings.
The most important qualification for being president is to not want the job.