I travel across the Corn Belt between Michigan and NE Oklahoma several times a year, and see the kind of "trailer got away from me" wreck you described on almost every trip between June and August.
But not in the mountains, on my routes the roads are flat and mostly straight. What the wrecks have had in common is that they've been on two-lane high-speed (55+) highways were folks often try to drive 5-15 mph over and do a lot of overtaking, and the tow vehicles have been relatively small, usually compact and mid-size SUVs, with TTs close to or exceeding the empty weight of the TV (but not necessarily its "tow rating").
I think some of these out of control situations are induced by other drivers. People towing on these roads have to be wary of those who overtake them (and often cut back in close and brake to scrub of their overtaking speed), and the bow waves from oncoming large vehicles.
I've towed since the early 60s when we were using 4000 pound station wagons, but the TTs were more often around 2500-3000 pounds (just sleeping boxes). We did not have much of the Interstate system yet, highway speeds were often 45-50 mph, WD hitches were just starting to be come common, but no anti-sway. Even with these easier environmental conditions, we had to learn to drive like we were towing, and how to use the trailer brakes to manage sway at the first sign of a problem.
I think people get into this without understanding the risks and learning how to handle them. Most are lucky, and do not encounter the conditions that start them swaying.
But experience doesn't guarantee one is ready.
One of my RV club members lost his 5000 pound TT being towed behind a 1500 HD pickup when he started a lane change to avoid being hit by a motorcoach doing a bad merge from a superhighway on-ramp. Before it was over, the pickup was on its back, the TT splinters and s**** metal, in the median. The motorcoach driver stopped to look, then left the scene after checking that he had not made contact. This was at 65 mph (in a 75 zone), no where near the speed limit, but too fast for controlling a sudden move.
One of my relatives lost a TT recently to a gust of wind on the western plains, towing at about 60 mph, 26-foot, 6000 pound trailer behind a F-150 rated to tow 8000 pounds. More than 30 years RV towing experience, once the sway started it got out of hand before he could regain control. On this one, the hitch head broke rather than the TT taking the truck over with it.
