Well to answer your question at face value do you think that such people might be depressed? And when people are depressed often they over eat... and when you overeat you get fat, and if you happen to have a lot of Testosterone in your system the body is hardwired to put that fat on the belly.
So in fact a really genuine Trans-person who is, as a result, very depressed may well be the very person who does get fat prior to transition.
I'm grateful that, transitioning so young I did enjoy that hourglass figure for a number of years. Proof here: this is postop me at 24. I'm now considerably more ample - largely the result of a depression that I got when my mother died in the late 90's - and it's only because I had already been over a decade postop and on estrogen at the time that I didn't end up with a huge belly.

So I really don't think that any of us should denigrate or question others who, through no fault of their own, are less physically fortunate. This is after all a supportive place.