Do people hate toyohime or something she has less art than seiran and ringo.
They never really got pass the whole "Moon-Sue" persona given to them. Her sister has more pics because as overpowered as she is, she did manage to outsmart her opponents as well.
Toyohime suffers from being ridiciolously OP as well as being unnervingly snarky. Up to the point that it's hard to evolve her character beyond "I am so much better than you and if you disagree I have a fan that can literally pull you apart atom by atom.".
Although I would like to see more stories expanding their characters, if only because I don't want to leave them in the box of "infuriating OP characters."
If what ZUN said in SCoOW is true, SSiB wasn't really appreciated until some time later. Maybe the initial lack of fan focus made the sisters not very liked and as a result they didn't expand their fanbase a lot even if people would like them more today.
Also manga-only characters in general don't seem to attract a lot of focus on them, except Kasen. People often joke on the Aki and Prismrivers' unpopularity, yet Lunasa alone has almost as many post here as the Three Fairies combined, and the Aki do even better than that, coming close to Kasen.
As for the Watatsuki's reputation (which is what makes me like them, btw), i think fans today are much more tollerant of godly smug characters that make everyone in Gensokyo look puny. I didn't see anyone hating Hecatia for being more powerful than anyone else and going all "I'm super duper powerful and Hell is my bitch. They won't try to eat Gensokyo simply because i'm here".
Also manga-only characters in general don't seem to attract a lot of focus on them, except Kasen.
This seems to be the root of the problem. ZUN did say a while back he wanted to do more manga with the Watatsukis as they have rather playful personalities that haven't been hashed out beyond SSiB/Inaba, so hopefully we'll get that, especially with Forbidden Scrollery having been concluded. Toyohime in particular seems to not really care much about being around Earthlings despite her viewing them as other Lunarians do, so I could see her freely mingling with some of the more eccentric Gensokyo natives while Yorihime hangs back and trains or something.