Politicians tend to pay attention to those they hear from (the "squeaky wheel" theory). The people who most have their ear have, at a minimum, cushy jobs that allow them to take time off during the day to phone or meet with politicians (it's not even time off when your income depends on that politician's vote). Those same people also have enough spending cash to contribute to politicians or their friends and relatives and, often, the ability to create more cushy jobs for those same politicians and their friends and relatives (being known as a "job creator" has its perks).
This isn't even mentioning the .01% who can create whole astroturf organizations out of petty cash.
This recent article documents how divorced most politicians are from their constituents - in both liberal and conservative districts. As we become organized, we begin countering this influence.
More on what happens then later..