Why do some breastfeeding moms still chubby/fat when ideally, they should be losing weight?

It happens because every woman has a different body and different metabolism. Some women during pregnancy gain lot of weight and their body layer up on extra fatty tissues, upwards of eight pounds. So, they already have enough fat stores to begin breastfeeding, on top of which they go on to eat more fat and high calorie diet to make up for the milk production. It happens so, that some women have high metabolism rate and they happen to burn this fat soon while others take time. So, eventually, women who keep a tab on what they eat and have high metabolism activity tend to get back in shape fast as compared to women who have already gained too much of weight during pregnancy and also their metabolism too is slow.