Oh, they did, in their way. There was no doubt that Ebisu-sama was using ayakashi- they found the masks, Ebisu-sama was blighted, hell, he used ayakashi right in front of all of us.

They just don't think anyone else was involved. The evidence on that point has been carefully concealed by the real sorcerer, I bet. [Not that that hasn't stopped the other gods of fortune being cast in a bad light. (It's hard to not hear things sometimes. People in Takamagahara can be such gossips.)]