Weight loss for some while EBF

From reddit research lol I’ve found that for some women they lose weight while breastfeeding but others gain (or not lose) it. I’m wondering why this happens to only some of the population.

Apparently prolactin is involved with weight retention and hunger levels, add in sleep deprivation and Ghrelin and it makes sense some women gain weight postpartum.

From an evolutionary standpoint it makes sense that the body would hold on to fat reserves while breastfeeding especially since that would have evolved during times where frequent meals were not guaranteed; so why then do some do the opposite of that and lose weight? Hopefully there’s research out there beyond “it’s just variation” because I find this so fascinating.

And I’m invested from a selfish perspective. Always been around 50-55kg (110-120lb) my whole life without ever watching what I eat, active lifestyle but nothing crazy. Now PP I’m 68kg (150lb), walking everyday, yoga at least 3 times a week and short Pilates sessions every other day and the weight is just hanging around