Due to the miracle of modern technology, you're able to enjoy snacks today that were manufactured on the other side of the country, but this also means your chips have to make a long, bumpy journey before they get to you. From the packing process on the factory floor to the shipment across America's pothole-filled roads, your chips take a hell of a beating from the time they leave the processing plant to the time they arrive on the shelf of the liquor store you're drunkenly perusing at 3 in the morning.
"The shit I've seen, man."
In fact, without all that air, chip packets run the risk of exploding if the truck drives through a high-altitude area, because physics is a freak like that.
Finally, the air in the bag isn't just regular air like you're breathing right now -- it's nitrogen. This preserves the chips on their journey, because exposure to oxygen is what makes things go stale. All things considered, if snack companies conceded to the public's demands and filled chip bags to the brim, then you'd be eating a bag full of stale potato flour right now, so be thankful for those depressingly under-filled bags. And now, if you'll excuse us, we have to go accept a comically over-filled bag of money from Big Salt ...