The processing time for a petition depends on a lot of things. Most important thing of all is filing it right the first time. They have to account for how many they process per day. Then there's the adjudicator that has a bias against you for some reason. To deny that this happens is to put your head in the sand.
People are people.
Some adjudicators detest what you are doing. Should you be unfortunate enough to draw such an adjudicator, your petition could sit there a lot longer than some who drew a better one. Then there's the workload. Sometimes a particular service center is swamped. Sometimes they're not.