These are people who lost 15 kg or more (33+ pounds). Most likely they were pretty overweight to start with.

And the heavier you are, the easier it is to lose weight because it takes energy to just maintain all that extra body weight.

Point being, there are certainly some people would not lose weight on 2000 calories/day, but I would guess that isn't true for most of the people in this study.

> And the heavier you are, the easier it is to lose weight because it takes energy to just maintain all that extra body weight

Well, the higher a calorie intake you are likely to be able to maintain and still lose weight, which is very much not the same as “the easier it is to lose weight.”

OK, I've got to admit that what I wrote was a bit ambiguous. I meant physiologically, it's easier to lose weight. But when you are starting with a group of people who are overweight to begin with, there are other factors like behavior or psychology.

Or if you're small. I'm 5'2, so even adjusting for physical activity my BMR is about 1600 cal. 2000 cal/day means I'm going to gain about a pound a month.