double the weight, double the cost, the extra scope barrel would dangle off the top of the rifle to snag on things and generally get in the way. the binocular scope would have to be canted severely so you could see through it while shouldering a rifle. this would require that the angle of the reticle could be adjusted to suit individual shooters. like regular binoculars, you would have to be able to adjust the width for different users. this would mean that the reticles would have to be independently adjustable, and you would have to align them separately buy exactly (or just have a reticle in one barrel).
other than range finding, I don't see how a binocular scope would help you hit a target... and they already have range finder scopes with fewer complicating factors.