Maybe it's that it's an abstruse type of game where those kinds of concepts aren't readily known? At least for me, geometry has never been my strong suit so when I tried it, the pictures started looking like things that confused me more. There's not a lot of context other than a find/match game. So it could be that people are only playing one level because it's too difficult to get immersed in it, rather than it's not too challenging?
Having said that, I really liked your mechanic of switching up the cards after a certain number of moves.
*edit: "aren't"