I know a few girls in the industry who suffer from PCOS (myself included).
PCOS makes weight loss quite difficult, though I did manage to drop over 20kg as my weight is a great concern for me, especially as I would like kids at some point and being overweight with PCOS makes conception difficult. I'm still 110kg (17st-ish) and despite cutting my calorie intake and upping my time working out I can't seem to get past that weight. My GP is going to be putting me on a course of meds used to help diabetics lose weight so hopefully I'll make progress.
I don't think WGs need to be any more concerned by their weight than their civvy street counterparts, but sometimes after a hard day, or a boring day I feel the chocolate cravings return, though that was true of before I was a WG too.
There is always the fact that BBWGs don't need to concern themselves with weight in order to get sex and the confidence boost from clients who find them attractive just as they are could make some girls want to keep their weight. I've even had one client leave me because I lost too much weight, at 130kg (20st) he was encouraging me to gain weight, which I think is wrong.
A girl I've worked with recently went from a size 14-16 to a size 10-12 and she is so unhappy, she hates her pics, she hates not being able to find nice clothes in her normal shops, she hates not being able to eat what and when she wants.
I would like to get down to 85kg (13-14st) and be a dress size 14-16 and I will be very happy indeed. I'll still be classed as obese by the BMI but you can't please everyone lol!