>>3938566
In the case of Higurashi, it is because a lot of the original official art was done by Sakai Kyuuta, the character designer for the series, who is a big yuri fan and has also done the character designs for a number of actual yuri anime (Strawberry Panic, Sakura Trick, Kase-san, and Sono Hanabira). The more recent stuff is probably just following suit since it is popular with fans.