I know that it can seem like hiring managers have absolutely nothing better to do than drive you slowly insane. I am here to personally assure you that as a hiring manager for 10 years, I definitely had much better things to do than torture job applicants. Let's look at the hiring process from the company's perspective.
A job opening comes about one of two ways, either someone has left the position, or a new position is being created. If it is an existing position, and proved over time that it is an essential role that needs to be filled within an organization, the hiring process can go relatively smoothly. The job description is in place, the budget is in place, and there is even a desk and computer ready to go. There can still be bugs in the system though.
First, the hiring manager has to have time to submit the job posting, and review the applications. The Human Resources department can help, but in some cases, HR is not a full time function in an organization, or many not even exist in smaller organizations. If the hiring manager is doing what they were hired to do, as well as fill the shoes of the person they're looking to hire, they are doubly swamped and will have trouble carving out time to search for someone. Second, depending on the hierarchy of the organization, the hiring manager might have to schedule the applicant to interview with several other people in the organization. Getting that much time on a set of people's calendars is difficult to juggle. Vacations, business meetings and unexpected family emergencies wreak havoc on conducting the interview process in a timely and efficient manner.
If it is a new position chances are that the hiring manager and HR department have put together a job description for their "ideal" candidate. Since they have never hired anyone for this position before, it's a little bit of guesswork if there will actually be candidates who meet their set of criteria. They could post a job description, bring in candidates, but realize that the types of candidates who are answering the ad are not exactly what they are looking for—so they have to start over. Also until a person is actually holding a position, there is always the chance that the budget could get cut at the last minute, or the search gets put on hold indefinitely.
Bottom line—it's not always your fault. There are many, many other internal forces at work throughout the hiring process—those were just a few of the more common scenarios. Hiring managers will be receptive if you respect their time and don't pester them during the process to ask about the status of a position. Sending a brief email or leaving them a voicemail after hours is a gentle way of keeping in touch that shows your interest without interfering in their day. Being patient is difficult, but necessary to maintain a good impression in a company's mind.