Because it was manipulating the air flow over the rear wing, and the FIA wasn't keen about it because of DRS. They were concerned that teams would try and use shark fins to passively stall air flowing over the rear wing. But with the rear wing being reprofiled - mounted lower and further back - there is less ability for shark fins to manipulate the air flowwhy teams weren't using it before ?
Voted "Ok" as some look great but others are executed horribly (cough Force India cough).