Why are AntMiners' firmware closed-source / non-GPL? What does Bitmain have to lose by making the source open?
The ASIC "arms-race" is all about having cutting edge technology. In a recent Motherboard article about a mining farm, the hardware was not even allowed to be specified.
Consider also that both SHA256/Scrypt ASIC manufacturers were clamoring to bring smaller nanometer sized chips - and the associated R&D costs - and it's probably more a question of why a company would make their hardware open source.