It's all about who these politicians perceive as their constituents. Most tend to care more about the companies whose money got them there, rather than the people that directly got them elected. This tends to sway them more towards their donors than their actual voters.
Consider that Barack O'bama got 70% of his election money from wealthy campaign donors. You get a sense of why he hasn't done enough for the American people, and his approval rating is at around 27%.