Because Scout engines are basically boat anchors. Way too much weight for the power they put out. That ones also a chunk larger, longer, and heavier than the Binders people normally wheel and Binders in general are like XJ's in that they require a lot of lift in order to go up in tire height.
Save yourself some headaches and look for an AMC-powered Binder. It shares a lot more mechanical compatibility with CJ's than it does with other Binders. Parts are a lot more plentiful.