What even makes these games so called "Bad" or "Ugly"?
Probably some mixture of hideous models with bad anatomy, terrible lighting, terrible camera angles.
Daz models limiting the devs ability to be creative, you only have models someone else made to use vs unlimited creativity of 2d art.
No gameplay or interactivity VN's, grindy or poorly guided progression.
Ancient game design where you're given a choice to peek someones ass or while they shower for 1+ corruption points.
Themes like every women, who looks like a skeleton wearing skinsuit, existing for the sake of being part of mc's harem collectathon, and since the dev can't write for shit they just keep adding more girls to collect so they don't have to build up existing characters relationships.
Ultimately its lowest common denominator bs, thanks to the nature of things these games can push out more mediocre content than other types of games and people go "sweet, more slop".