I'm not sure where you're seeing mostly skinny trans women, but there are some of us out there who are less so.

I'm around 220, and that has actually been an advantage in some ways - I'm very curvy and big-breasted and my face is nicely soft - and hasn't really been a significant disadvantage. (My surgeon agreed that health and fitness level was more important than weight, too. I managed to lose maybe 15 lbs for surgery as a side effect of getting as fit as I could, and I had an excellent and quick recovery with good results, so weight was in fact not an issue.) I might prefer to be thinner, but I'm in very good health and mostly happy about the places the fat went, so...