Not American, but as someone that works in local government, it's usually a combo of:
1) Processes that haven't clearly been worked out, leading to buck-passing.
2) Massive levels of overwork, with huge caseloads sitting with far too people due to budget cuts (this is the big one) - especially an issue with people retiring/leaving, and their responsibilities being broken up and given to existing employees rather than re-hiring.
3) Occasionally, uncaring employees.
People always hype up number 3, but in my experience, too much work for too few people is the main one.
I do loovveeeee it though when people talk to me about public sector inefficiency before telling me the firm they work for employs three people for a job that one person does in local government.