The way the system is set up, most politicians don't think they have an alternative. Unless you're a standout star in a high-profile race, your election prospects are inexorably linked with your ability to fundraise (as well as your party affiliation, if you survive the primary). If you're not cashing checks, your opponents will.
It's the same argument you hear from businesses and affluent individuals: "If I don't [pay my employees as little as possible | take advantage of every tax loophole I can find | spend thousands of dollars lobbying congress | pollute the environment], my competitors will."
Of course, those excuses ring hollow when those same individuals aren't in favor of changing a broken system. Any politician that complains about fundraising but is not in favor of campaign finance reform is a hypocrite, IMHO.
