Name changed. I agree OP. I don't know where the 2000 calorie figure came from but it's been around for as long as I can remember and I'm nearly 50 so it must be war years data I should think, before everyone drove and before we had domestic appliances and lifts, escalators, travellators etc.
When I was a teenager and weighed 12 stone as 5'6" in the eighties and wanted to lose weight, I ate 1000 calories of good food for two months and bang, I lost the two stone. I tried the same again once I hit 30 and couldn't do it, I had to go down to 900 calories of good food (very few carbs) and it took three months.
Approaching 50, having struggled with my weight and topping 12 stone again, I again needed to lose it so went to see a specialist (dietician) about why I was finding it so hard to keep my weight on an even keel even though I did HIT (the shred) and walked/hiked a lot and ate proper healthy food.
I had my basal metabolic rate measured and it gave a reading of 1030 calories so in order to lose weight, I'd have to eat significantly under that and exercise. I've done it on a no carb meal replacement diet of 600 calories per day and 20 minutes of HIT every other day. I now weigh 10 stone again.
Some people just have a low metabolic rate naturally (going for a poo once or twice a week anyone?) always cold, sluggish, no energy. It's a give away. All those people who poo daily or more have high metabolic rates. I had my thyroid checked in case that was the problem but no, it was fine (three tests in total over 3 years). It's just the unfortunate way I am. Very unlucky. It's salad and chicken for me now until I die unless I want to gain weight again steadily as I get older.
I always used to wonder why the lissom middle-aged and older women in Kensington and Knightsbridge ate like birds despite being thin - now I know. My mum used to pick at her food as does my sister who's mid-fifties (both reed slim).
For some, 2000 calories will be fine and they'll stay slim, others can eat 3000 calories and stay slim. The more unfortunate among us have to be more careful - more so as we get older. That 2000 calories a day figure gives a false message of the quantities that women can eat without weight gain though, no doubt about it.