Do you have a source for that
If only we knew how many trucking violations the DMV has missed (and potential accidents could have been avoided) if they weren't:
"ticket-fixing, bribe-taking, on-the-job politicking and favoritism"
or
"often participat(ing) in statewide enforcement actions such as the seat belt campaign "Click it or Ticket" and the drunken driving crackdown known as "Booze it and Lose it..."
The other statistic you don't mention is that about 80% (according to the NHTSA) are caused by the actions of a 4 wheeler, the most primary of these being impatient and making an unsafe/illegal pass. IIRC the second most frequent cause is someone passing on the right.
Mechanical failures of any kind represent a small percentage of accident causes, far less than mechanical failures (mostly tires) involving passenger cars. If you don't think that DOT is doing it's job, just ask the owner of almost any trucking company how much he paid in fines last year. DOT here in /FL can and will invent violations and rememeber that all DOT fines have to be paid on the spot, in cash or the truck is impounded. Fines range from the necessary, to the ridiculous. I once paid a $150 fine for having an accessory light not required by the standards inoperable. DOT writes the lots of non moving violations because they don't put points on your CDL, and they know that truckers don't have the time to fight over small fines. Ever see those big barns at the back of the scalehouses? You can hear the cash register ring everytime they deign to pull some unfortunate soul into one. DOT gets to keep all of the revenue from the fines they generate instead of putting the money into the general funds to be doled out come state budget time. Think that might provide an incentive to write someone up?
Professional truckers drive grossly more hours/miles without an accident than your average motorist. It's obvious that many here have some story to tell, but by and large the goods get delivered safely. If you heard about every 4 wheeler that did something stupid, FR would be out of bandwidth.
Next time you purchase anything, anything at all, remember how that product eventually got to the market. It got there on a truck.