Well for one thing, women these days, especially younger women are taller and heavier than your average 1950s housewife, so simply existing burns more calories.
I'm 45, 5'7", weigh about 12 stone 4 and the TDEE calculator gives between 2000 and 2200 calories burnt per day, depending on whether I am lightly or moderately active, I would say lightly active.
I'm not much more than average height or weight, but my job is about half in an office and half quite, but not very active, so not like a nurse, postwoman, warehouse/retail worker etc. I don't go to the gym, but do a bit of walking and running. I definitely eat more than 2000 calories a day, which is why I'm overweight.
Younger women, those with active jobs, or those who do a decent amount of exercise, are likely to burn more calories than I do. As someone upthread has indicated, you have to be very light and sedentary, to burn significantly under 2000 calories a day, which is why the average is still 2000 for women.