Dunno why people are thinking Aya does not realize what her feelings for Mitsuki are, the "Can I think Koga-san likes me? No, no way, way, no way, but still" on page 4 pretty unambiguously conveys she's thrilled at the idea of Mitsuki liking her romantically and is trying not to get her hopes up while still being very excited at the thought regardless. Aya knows what she's feeling and what she wants, lol. She'd kinda given up on Mitsuki liking her back after the big romantic rock performance that climaxed with "will you be my friend" but now she's over the moon at the thought that things might move in that direction instead of continuing platonically.
If anyone doesn't fully realize what she's feeling yet, it's Mitsuki. But we're getting some major hints of evolution from her now :3
People have just had bad experiences with manga in the past. What seems obviously the case has sometimes not mattered, so some probably want really explicit confirmation before getting their hopes up.
I would say that in my case at least it’s far less about the fear of yuri-baiting than it is the fact that this series requires a lot of inferences about exactly what the characters are feeling at any given time and what they understand about their own feelings and the feelings of others—the whole series is based on a pretty big (and fairly extended) misunderstanding, after all.
Not to mention that Koga is so dense that even if Aya took out a billboard that said, “I, Aya, have romantic feelings toward Mitsuki. Also, FYI, two girls can have sex, and I want to have it with her,” Mitsuki would find a way to think it meant something else.