Malvineous:
Out of curiosity, I did a search on Feabie for women who like men who are "chubby with a belly", and got 7,793 results out of a total 19,424 women who like men in general, making it 40.1% of the total.
I repeated the same search on Grommr for men seeking men with the same body type. It returned 23,921 out of a total of 50,186, or 47.6%.
OP does have a point. Not only is the percentage higher for men by almost 8 points, but the gap between 7K women and 23K men is huge. It's no surprise that more men are in these communities than women, and combine that with women generally not making the first move and being more cautious than men online, and they're going to feel rare in comparison.
This data is less about different genders that like chubby people with a belly than it is about women who are comfortable enough to admit it on the platform they are on.
Basically, it's apples and oranges.
It also doesn't take into account plus-sized body types like chubby without a belly, morbidly obese, strong fat etc., etc.
It would be interesting to see a robust demographic study on the online feedist community. Unfortunately, despite all the attempts I've seen to make such a thing, the engagement has been piss-poor.