Because Enterbay will already have made 2 versions and I'd be very surprised if they went back and made a 3rd semi damaged Cyberdyne version. 1/4 scale is expensive so I can't see them dipping in a 3rd time.
Which would mean the minigun would be basically the only thing missing.
And for those of us that intend to buy both, we'd have all the parts necessary to make a perfect Cyberdyne minigun version ourselves if they do choose to include the gun.
...plus its a way to tip people over who are on the fence about buying (especially those that own the first one)