Restraint systems are often pointed among the most important safety features in a motor vehicle since the first lap-belts were introduced by Volvo in the 50's, and their complexity increased considerably after the introduction of 3-point seatbelts and airbags. A simple lap-belt is still enough for the driver and passengers to avoid having their necks broken in case of rollover, while a 3-point seatbelt is only useful either if it's the only way to prevent the driver and front passenger(s) from hitting the windshield in case of collision or to enhance the support for disabled drivers. Airbags, in spite of all the hype around them, don't really seem to make so much sense.
Restraint systems would be less likely to save anyone's life in a structurally weak vehicle, such as some third-world econoboxes which bodies are made out of lower-grade steel alloys and often thinner metal sheets, while their counterparts targetted to developed markets might easily fare better in case of accident when a defective airbag wouldn't deploy. Actually, even a side-by-side ATV such as the Polaris Ranger is safer than many third-world subcompact cars. It's also worth to look at American school-buses, which are fitted with lap-belts in a few states but usually don't have seatbelts everywhere else while still deemed the safest road-legal vehicles on earth. The concepts of "compartmentalization" applied to their interior layout sure has an important role on that matter, while the side panel trims and seats cushioning provide different grades of impact absorption in order to prevent major injuries while the seat backs height prevents whiplash without resorting to airbags, and not even the simplest lap-belts are needed if we consider that a school-bus is not so prone to rollovers.
Having such examples in mind, what can still justify the cost and complexity associated to airbags? Basically, sophisticated restraint systems also work out as an easier excuse for the marketing departments of the manufacturers to push more expensive options for customers who don't really need, neither want them. That way, the extra cost coming from a pair of airbags may seem more diluted at the price tag of a car with a fancier interior trim, infotainment, alloy wheels with fat low-profile tyres and the hell out than it would do in a no-frills version with manual windows and mirrors, plain-black mirrors and door handles, a cheaper trim, skinny high-profile tyres in smaller pressed-sheetmetal wheels (with or without hubcaps) and a simple AM/FM radio with USB connection (or eventually no radio at all). Even if the profit margin at the airbags and the amenities gets a slight reduction in order to be pointed out for the final customer as a "value package", they're still highly profitable for the manufacturer due to an increase in their production volume.
Another matter of concern, regarding most specifically to airbags, is the clearance issue while fitting the vehicle with adaptive controls for disabled drivers. Some interfaces, such as ring-shaped accelerators mounted over the steering wheel which are still widely popular among paraplegic drivers in Europe, were already challenging when driver airbags started to appear, and revisions on their designs were required to overcome this difficulty. Nowadays, knee airbags pose a major issue regarding lever interfacess, either just for the brake or combined accelerator/brake units. Some popular devices in this category still use pushrods to transfer the movement from the lever to the pedals instead of cables due to reliability concern, but it ends up on the way of knee airbags when they're fitted. Altough it might seem easier to just resort to a floor-mounted unit such as a Carospeed/Menox, any one-size-fits-all approach to this market segment won't work out so effectively.
We can't deny the importance of safety features such as ABS brakes and stability control, since they effectively decrease the likelihood of a crash, and collapsible steering columns for avoiding many deaths, but at a certain point airbags get excessively praised, and it's not so inaccurate to claim that seatbelts are also over-estimated at a minor extent. Apart from the noticeable increase in the purchasing cost of a vehicle fitted with airbags, the cost to get them replaced, either due to deployment or expiration, is rather unjustifiable considering the residual retail value either in an older car or in a salvaged one, leading otherwise roadworthy vehicles prematurely to the junkyard.