I was reading the thread about spreading ganache under fondant, but I wanted to know why you can't just pour ganache onto the cake, let it set, and then add the fondant?

Also, I'm making a sand castle cake, and it seems that pouring ganache would be 100% easier than spreading BC. Once the frosting is on, I will be adhering crushed nilla wafers/graham cracker crumbs to it. Am I wrong to think the poured ganache would be easier to get into all the crevices?