It’s because of the major webnovel website having exactly that issue of only the title to go off. Lots of LNs are then based on/republished from webnovels and I guess from there it started propagating a bit to other media. Though the VN mentioned in the title seems to be a case of an extended rerelease, the 2 years older original didn’t have the long subtitle. (vndb.org/v4857 nsfw text duh)