Why did Ayu become popular?

[tenshi no hane]

^ Actually, she does somewhat think "she was at the right place at the right time" She has stated in older interviews that she's simply lucky that her lyrics and persona resonate with her generation (at that time).

She mentioned this in her recent interview on NHK SONGS 2015 too. Delirium-Zer0 posted subs in the Downloads section:

Commentator: The things Ayu wrote about were the anxiety and isolation that she herself harbored. The girls of her generation sympathized, building her into a charismatic popular figure.

Ayu: [...] when I debuted I'd sing about how I didn't have anywhere where I belonged, and that seemed to resonate with girls who were living through the same era that I was.

Commentator: From "sympathy" to "resonance," and from "big hit songs" to "social phenomenon."

edit: And great, insightful post, Delirium!