Maybe it's corruption, but my guess is it's just never been important enough to push through. Imagine all the work that would go into phasing out coins, both politically and logistically... all for what?
It's not corruption. It's what I'll call the interest-group problem.
Pennies are an issue a few people care deeply about and most people don't. It's electorally thrifty to accomodate those few, and so electeds do. It's an easy win, particularly in a partisan environment that punishes consensus building as betrayal of one's base.
Put another way, keeping the penny won't piss anyone off enough to get one primaried. Killing the penny might.
I imagine it would cost less than all the money collectively spent on minting them and buying and maintaining machinery to handle them. Even better if they got rid of the quarter too. But yeah, I can see why no politician has decided to make this their signature issue.
