I would point out that the B757 is not a type rating by itself, it is a B757/B767type rating and with preferably a differences course between the two included in the training.
The B767, moreso than the B757, is a year round aeroplane, when Europe gets cold the punters still want their holidays in Florida, Caribbean, Far East etc. thus it is not a 'seasonal' aeroplane unlike the shorter haul A320, B737 etc.