it's not so much a myth as outdated data. when they started figuring out the nutritional info in foods and how many calories people needed most people weren't working desk jobs, playing on the internet and watching tv for sixteen hours or so a day. and they haven't quite gotten around to updating the info. i'm not sure if you have ever looked for weird laws still on the books in your area [in my area trains aren't supposed to pass through town faster than a man can walk. that does not happen, but the law still happens to be on the books], but this is the same thing. it once was the standard, but nobody has bothered to go back and update the info.
that being said most women have bmrs in the 1000-1600 range, depending on their age and height. add in basic daily activities [20% of bmr] and you're looking in the 1200-2000 range. the 1200 side is going to be for those shorter or older and the 2000 side is for the younger and taller.
your spark ranges are loss ranges, so comparing those to that 2000 cals isn't accounting for the fact that that gap between 1550 and 2000 cals is what is making you lose weight and burn the excess fat that's in your body instead of getting the energy from food. in other words, if you are set to lose a pound a week and you're getting a 1550 number, that means that to maintain your weight it would take 500 cals more than the numbers provided, or right about that 2000 cal number.
and that 2000 number is an average. not everyone burns the exact same amount of calories. which means that the more active women are burning closer to 2500 a day and the more sedentary are burning more like 1500 a day. whichever side you are on, it still averages out to 2000. or at least somewhere close. 2000 cals seems like a much rounder, nicer number than 1879 or something else that might put people off from doing any calculations on the topic.
-google first. ask questions later.