... or do they think ...
In my opinion, the problem is they don't think at all before starting a maneuver with their car.
HTR, that is probably true. I know that before I started driving our bus, I would open a "decent" amount of space between the vehicle I'd passed and me before pulling back into the lane. Since driving the bus I now open probably twice space, or more, and continue to accelerate when pulling back in to keep a healthy buffer between my vehicle and the large one behind me.
Something I have noticed is that if after I have passed a truck, then activate my turn signal, but continue to stay in my lane, some truckers will signal when they feel there is a big enough gap. Most times when I bothered to pay attention to the rig, they appeared to be O/O instead of company ones. This, however is a rare occurrence. Bus drivers that I have encountered are either passing me, or running up my tailpipe, and I'm usually running 75 mph.