I don't know why anyone would expect a vehicle to pull off onto one of those just to let people pass.... So weird. I'd expect that to only be for someone who actually wants to stop and take a rest or something.
Oh I dunno maybe because it’s courteous and not selfish, or maybe it could be because posted signage often informs drivers that it’s Mandatory for slower vehicles to pull over if x number of cars are following.
Yeah why would people expect anyone to do that?