Most people don't drive defensively, courteously, or safely. When they drive around big vehicles their bad habits just amplify the consequences. It's pretty typical for people to drive in a truck's blind spots by either following too close behind or driving where the mirror's don't have much coverage. Also, many drivers don't seem to understand that trucks have different limitations in driving than cars. Typically I try to avoid driving just behind a truck (even in a neighboring lane) and I try to avoid being side by side with a truck for long.

In my experience truck drivers are generally better drivers than the average non truck driver, but they certainly aren't perfect as a group.