Another way to look at is ask why do the wheels do that, why will they not hold “center”?
A wheel in motion tries to find center, with DW it goes to center, then beyond, then tries to center, and goes beyond- over and over- this IS death wobble- the main forces at play are the tire rotations’ gyroscopic force and tire balance-
If the imbalance is greater than the tracking force- bam, DW
If linkage or control arm (the track bar is also a control arm) play allows movement and defeats the tracking force that holds tires steady, it means less tire imbalance, or just a hard lick, can cause DW. There is some relativity going on- you have multiple components, usually of various age and condition at this stage of the game.
This describes the majority, but not all.
I know of a case where a brand new brake rotor was causing it.
It is not a vehicle design defect, it is a result of forces or wear defeating and or simply tire imbalance overpowering the design.