I had a summer job that required me to drive a 4x4 Suburban that did this, it was very hard to control when the front end started that high frequency, vibrating wobble. It was stock as far as I knew, late 70’s model. I just attributed the problem to age, mileage and wear.
This particular problem is specific to Jeeps. The vehicles that suffer from this have a bolt in the steering linkage that's too small for the hole. To compensate, it's torque'd to 135ft/lb(which is a LOT). Once it wears a little, the front end can floppy around like a fish.