If I remember right, you couldn't see any content on Imzy without creating an account. I assume that instantly turned away over 90% of the users. Then, their design was extremely childish, and it looked like a safe place for kids, rather than a site for adults to socialize. I think they did a really poor job at understanding the market, and I'm not surprised they failed.
https://i.imgur.com/9uzaciS.png