They may have been quiet days but look how many Britannia flights were going in/out across the day - far more than the paltry TUI flights today
BY's sizable flying program from LTN ended in 1993 with the withdrawal of the hard-working and flexible 737-200 fleet. Aspects of the program such as the MOD flights to Germany were never going to continue on the 757/767
so of course these ceased and the base reduced to 2 x 757's as flying from other airports increased.