Why did the airbag not deploy on Statham's Maserati in Furious 7?

Cars before a certain year (1998) are not required to have drivers side air bags. And there is a loud majority of modders in car culture who believe air bags are more dangerous than life saving, and will remove airbags from a car in that respect. It's not unusual for a souped up car to lack air bags.

From the Emergency Medical Journal:

Airbags have been shown to significantly reduce mortality and morbidity in motor vehicle crashes. However, the airbag, like the seat belt, produces its own range of injuries. With the increasing use of airbags in the UK, airbag associated injuries will be seen more often. These are usually minor, but in certain circumstances severe and fatal injuries result. Such injuries have been described before in the medical literature, but hitherto most reports have been from North America. This is the first case report from the UK of serious injury due to airbag deployment and describes the case of a driver who was fatally injured when her airbag deployed in a moderate impact frontal collision where such severe injury would not normally have been anticipated.

Air Bag deployment will often knock someone unconscious, and while life saving, there is a rare case of fatal injury, from the deployment itself. You have an exploding, rapidly expanding bag of compressed air flying towards your face. Like a Mike Tyson right hook. Strong enough to throw a 200 pound man in the air:

They can also trap you in the car, which can lead to complications in a fire.

That said, the 2014 Maserati Ghibli has multiple front and side air bags standard. Many people have noted the missing deployment. There is no dialog explicitly stating the airbags were removed, but the dialog right after the crash implies modifications:

Dominic: Reinforced your chassis. Just like going into the ring with weighted gloves.

The implication of modifying gloves to cheat in boxing.