Why is there no response after an interview?

I have had many interviews (telephone, onsite and in some cases second interviews)and in most cases I do not receive any response from the interviewer or company. Obviously, if I get the job there is a positive response, which hasn’t happened lately, if I don’t get the position there is hardly ever a response giving me any information. I have actually tried contacting the interviewer and still have not received any information for months, even after trying multiple contacts.