[@BingTheWing], what [@DeadDrop] said.

Official reasons may include: contagious disease carrier, harboring extreme ideologies, possessing dangerous goods, criminal background, lack of a productive job, not fluent in English/Hindi/Odia, having too many family members/relatives, faking personal information and more

There is also a quota of "released" Kashmiris and Bengalis each month. If an official manages to hate an applicant at first sight, they can come up with bogus reasons like "didn't fill out form properly".