What is it? Simply it is the failure to grasp the concept that it isn't just polite, or dignified to give people room to let people get off the tram before getting on, but it is the efficient way of doing it. Whereas crowding forward round the doors of a packed tram and indeed actively resisting other people's attempts to alight makes the whole process longer for everyone. I really don't get it, even if all these people believe they have a divine right to be on the tram right this second, none of them actually seem to be divine enough to walk though those comming off the tram. Also if they were omnicognisant they would realise that at the very least some kind of interleaving rather than moving forward as a Spartan phalanx (admittedly with tuting rather than point spear death) then the whole thing would work so much better.
If it was just an extension of the "mall" induced arrogance of the modern pedestrian and their belief that they can set a strait line course and not have to deviate for anyone then wouldn't it be the same everywhere? Is Meadowhall so much more a nexus of evil than other similar places that Sheffield suffers more than other places? Will it evolve so that as well as tram door blocking and the use of pushchairs containing infants to stop traffic the citizenry will start to violently remonstrate with street furniture for getting in the way (above and beyond the special brew chugging types that are already doing so, but being an underclass, they aren't allowed to count).
This urgently needs someone to put together a research package to find a cause and a cure, before I give into my temptations to start taking a battle axe to work.