From Roll Call:

“Members of Congress are very frustrated — we saw record numbers of them quit last year,” said Kevin Kosar, a leader of the nonpartisan Legislative Branch Capacity Working Group and vice president of policy at the R Street Institute, a think tank with libertarian roots. “Politicians like to go to ribbon cuttings, they like a sense of accomplishment. And earmarks are a way to do that. It provides a way for them to directly claim credit for making something better in their district.”