I have found over the last few years that fewer and fewer truckers will blink their lights in appreciation after you flash to let them move over.
I am with some other posters - so many people simply don't know about driving "rigs" (big trucks, campers, etc) and what they need for room, speed, etc.
In my town when a delivery truck needs to pull out or especially back into an area, cars will just continue to zip around it not letting it move. It usually isn't until someone in a pickup truck (or larger truck) stops traffic that the delivery truck can maneuver.
Too many are just not paying attention to the world around them. Similar to what has been said, it seems that paying attention distracts them from texting...