Incomplete or inconsistent filings
Missing signatures, missing translations, missing fee amounts, and answers that conflict with an earlier application are the ordinary causes. Each one generates a request for evidence, and each request adds months.
Requests for evidence
A request is not a denial, it is a list of what the officer found thin. Answering it fully, the first time, matters more than answering it fast. There is a deadline, and it is not extended.
Visa availability
In preference categories a case waits for a visa number. That wait is set by the category and the country of chargeability, and it moves. It is not a processing problem and cannot be sped up by inquiry.
Background checks, interviews, and transfers
Security checks, interview scheduling, and files being transferred between offices all add time. Keeping your address current and responding immediately to every notice is the part you control.
