I hear what you are saying in spades.
If traffic conditions have changed I do wait a bit to see if there is any change to the driver’s speed, then if I’m sure that’s his lot I move out. A Howdens Joinery driver springs to mind as someone with no idea what is going on around them, looking idly at my cab as I try in vain to get past him, even gesturing to him in a ‘what are you playing at’ style only elicited a reply gesture of ‘well you should get a move on then’. I gave up and tucked in behind him.
Lorry drivers are now as crap at driving as car drivers, the quicker you get used to this concept, the sooner you can attain inner peace.