@ALfromHELLSING I think partially it's because of that plagiarism accusation, but it is weird how the song is neglected by her. I remember of how surprised I was when she didn't sing Yume no Uta at the Premium Night. I don't think songs such as Pearl Moon, flower or even Rain are more popular than Yume no Uta.
The song is a total rip off, but it doesn't take the shine away, it's a gorgeous song.