It'd probably because a) they're starving for representation and b) it brings something fresh to the fairly stale love triangle tropes.No matter what yuri story I read I find the poly people pushing their agenda...
I am calling it now. Erika either killed Aya or did something to make her disappear. She has motive and knew where Aya was going and at what time. She did not seem sad at the reunion either. She was more observing.