The biggest issue with yuri is that they recycle the same settings. School girls have been done to death, and while there are occasionally some nice twists within the school girl genre.. it's not enough to make up for the fact that school girl still reigns supreme in yuri. Especially when you consider that a lot of the yuri we get is one-shots.. doing a story in a school setting is quick and easy. It takes more work to make something unique and interesting like sci-fi, or fantasy..
The last few yuri anime released have been school girl as well, but some had good appeals. Yuri Kuma took a fantasy setting about bears, and Akuma No Riddle was about girls trying to kill each other. If people wanna do more school girl yuri, we need more interesting stuff like that. (I'm also not counting valkyrie drive mermaid. i didn't watch it because it looked like a male-gaze fanservice nightmare)
We need more adult yuri, college yuri, fantasy yuri.. anything that isn't just school girls. It's heart-breaking looking at amazing yuri series like Flower Flower, which had gorgeous art and enjoyable characters with an interesting story that was slowly building up.. only for it to never get finished. But we get an endless supply of school girl yuri. School girl series are the mcdonalds of yuri... cheap and easy.. we need more quality food.