The fact that Liverpool and North Yorkshire are both in the medium tier suggests it's not a north vs south thing.
Greater Manchester in tier 3 isn't too surprising. Cases are falling rapidly and the average rate isn't much higher than the national average, but it's overloaded with bars and restaurants in a crowded city centre and they probably think it will get out of control again in the run up to and over Christmas if these reopen next week. The region was consistently amongst the highest in rates across the country between late July and the second lockdown, not many other areas were so high and for so long.
The only medium tier areas are:
Isle of Wight, Cornwall, Isles of Scilly.
The divide is how the boundaries are drawn. Berkshire, Sussex, Gloucestershire and Somerset are among the areas where the tier level have been decided on the level of infection in a local council area, in the case of Berkshire that means only Slough is tier 3, rather than the whole ceremonial county. On the other hand huge diverse areas like Greater Manchester, Lancashire and the North East have one blanket restriction for every council area within that area. For clarity the London boroughs have all been grouped together and boroughs have been grouped together across the Midlands, as well as in the North.