I also agree some don't know they're allowed to. I was recently sitting in 1A on an American Eagle flight and the passenger in 2A was very tall and his knees were in my back. I suggested he might want to move across the aisle to the empty bulkhead row so he could stretch out a bit (I truly did feel bad for him besides it being annoying to me) and he gasped and said, "You're not allowed to switch seats!"