They said it's because the vehicle's windows were apparently tinted, and ticketing officers don't normally search cars.
The medical examiner's office said Friday that George Morales, 59, died naturally from heart disease.
The body was found in the backseat Wednesday when a city marshal tried to tow the vehicle.
It was parked beneath an overpass on the Brooklyn-Queens Expressway.
Police said Morales was believed to have been living out of the white Chevrolet minivan, which had North Carolina plates.
But his daughter, Jennifer Morales, 29, told the Daily News he had been living with her family in the Washington Heights section of Manhattan.
She said she last saw him in early May and had called police. But police say they do not have a missing person's report on record for Morales.
"The window was cracked open. I don't understand how no one noticed him. They just gave him tickets," she told the Daily News.
She said her father was a handyman who suffered from diabetes.
It wasn't clear exactly how many tickets were on the minivan's windshield when the body was discovered. Witnesses had reported a foul odour near the vehicle.
The Morales family plans to cremate the remains. Officials used X-rays taken of him in 2007 at Elmhurst Hospital Center to positively identify him, Jennifer Morales told the newspaper.