If I am not mistaken there were no aftermarket lockers for the front axle until a few years ago. I am not aware of limited slip being a viable option for front axles.
I have had a Ford Bronco (old style) and a Jeep with factory limited slip front axles. I have also had a CJ 5 with an aftermarket limited slip front axle. If you mean they aren't available, probably not. If you mean they are not feasible, you're mistaken.
