People frequently tailgate instead of moving into the next lane to pass, they frequently tailgate people who are in the outside lane but due to other traffic conditions cannot pull over. If i'm in a passing lane i will move out of it once i have completed passing the slower vehicles, and it will not be possible to pull over as there will be other vehicles on the inside.
Tailgating such a vehicle is stupid and dangerous, there is clearly nowhere it can go so wait for it to complete what its doing. If someone is sitting in the outside lane for no reason then it's still stupid to tailgate them as they clearly aren't paying attention to the road properly, and could easily be surprised causing them to brake suddenly.
I will leave the passing lane(s) when it is safe to do so, sitting close behind me is dangerous and it can't make me move over more quickly because there's nowhere to go, at most it will cause me to slow down in order to reduce the impact of a crash and increase the distance to the vehicle in front so i wouldn't need to brake so hard if something happened.
Something else i find extremely annoying, when you are following the rules and pulling in to the inside lane when not overtaking, you approach a slower vehicle ahead and want to move out, but there is another vehicle sitting alongside you or passing very slowly in the middle lane and the outside lane is clear. They should move out into the outside lane so that you can move into the middle lane, but they usually don't so you are boxed in and forced to slow down.