Just to clarify, a dangerous goods contract is not an exemption, it is a requirement to be able to ship more highly regulated materials. Shipments that require diamond labels, shipping papers, etc. Without a dangerous goods contract, you can ship dry ice, batteries, and consumer commodities, with limits to the amount that can be shipped per package.
I cannot comment on the shipments you have seen, but yes, some companies do not satisfy the requirements we have discussed, and other requirements as well. We catch these shipments at times due to poor packing (contents falling out) or damage to the outer carton that reveals the contents. We also watch out for flag words while processing exports, as shippers are required to declare the full content of their shipments.
The VAST majority of people do not know that hazardous materials (aka dangerous goods) are ubiquitous. Their main exposure has been liquid haulers displaying diamond labels, and failure videos on youtube. "Oooh, chemicals! That stuff probably explodes!". They don't know the difference between combustible, flammable, and explosive. They don't know what a diamond label signifies. They don't know that they are surrounded by
materials in their homes, even in their pockets, that are hazardous enough to have special regulations for transportation.
The majority of issues occur when a company starts shipping hazmat, starts shipping a new hazmat, gets a new employee, or has a low frequency..
1) New hazmat shipper. If you've never shipped hazmat, it's likely you do not know that you can't just breakout the bottles from that pallet of fryer cleaner you just received and ship out to your customers in umarked cartons. You don't know because you're a $9.50/hr shipping clerk and no one has told you otherwise, because the shipping department head is a $10.50/hr employee that was trained by the previous $10.50/hr shipping manager and does nothing to further his/her knowledge because $10.50hr.
2) New hazmat material. Shipping a new material that has different marking/labeling requirements than what you have shipped to date usually results in violations. Most companies that ship hazmat to end users only carry a handful of regulated materials, and they get in a knowledge rut of what they ship. See #4.
3) New employee. Most companies that ship hazmat to end users only send two employees to training, because $$. When one of their two trained employees departs for greener waters, they often will not send a replacement to training until they get notice their remaining employee is departing, leaving them with a freshly trained employee that has to learn the ropes on their own.
4) Frequency. We've got a handful of hazmat contracts at my operation that ship a handful of hazmat per year. If you don't use it, you lose it. Due to this, many take pictures of how their package should appear, which works fine, until the regulations change, or they get a new hazmat and think they can just duplicate the other package with the correct diamond label, or they think the same weight limit applies, etc.
All of this said, there are exemptions to marking and labeling requirements that the shipments you have seen may be in compliance with. Some are general exemptions that any can use, others are granted by the DOT/FAA to the shipper. The packages you saw may have had exemption markings or labels you did not recognize. For example, a carton may have a pre-printed DOT-E exemption number on one side.
