I also thought the few FA creators is why Sumo wrestlers are presented as ugly/comic relief in most anime/manga. If most of them have ugly/cartoony faces because most creators don't know how to draw plumper bodies as sexy/attractive and that includes faces. I know there are sumo fan girls IRL, just figured that most mangaka aren't interested in the sport and may not know of them or are interested in having them in a story or catering their manservice towards them, they'd rather have ripped dudes with 6 packs over presenting sumo wrestlers being sexy.
I did wonder why no ecchi story with female sumo wrestlers. Figured it's that the sport is men only, the premise wouldn't be seen as sexy to most of a potential audience, even if it had thin curvy women, it would be seen as weird not sexy. Like if someone did a tale of lingerie/bikini women doing American football/rugby it would be seen as less sexy and more weird to a possible audience. I can buy that bara (works by/for Gay/bisexual men) are the exception to what I said. I'm sure there's bara works of hot sumo wrestlers and/or someone gaining weight to become a sumo wrestler being treated as sexy. Just figured a story where a woman gaining weight to be one wouldn't attract much of an audience, the same if one did a tale where a bunch of sumo women get into sexy situations or have a sole dude getting into sexy scenarios with them.