Looks like their engineers decided on a frame side drop for a 2-3" lift and an axle side for a 3" or more lift.
Some other manufacturers have done an axle side raised bracket for the lower lifts that bolts on at the stock axle side bracket--resulting in too much leverage on the stock axle side bracket and eventual failure of the stock bracket welds.
The 3" or taller axle side bracket does not rely on just the stock bracket and stock bracket welds. It ties into multiple points and uses u-bolts around the axle tube to prevent failure of the stock axle side bracket and welds.
With just a cursory look at other manufacturers, most
use a frame side drop for less than 3" kifts and an axle side bracket for 3" or more lifts. So, their engineers must have come to the same conclusion as Teraflex.
I ran a 2.5" Teraflex BB on my 2 door for more than 12k miles and never had handling problems or felt unstable cornering or driving winding mountain curvy roads. So, I am personally satisfied that most
other manufacturers' engineers design their shorter kits that way for a reason--other than some attempt to purposefully push consumers to a 3" or taller lift.
Teraflex uses the axle side bracket with their 3" lift an anything taller--not just on their long arm kits. Here is their 3" kit:
As disclosure, we run a Teraflex 6" long arm with Off Road Evolution coilovers/King shocks/rear EVO lever system on my wife's 4dr JK.
On my 2dr JK, I run an OME/JKS/RE/Teraflex/Currie/Skyjacker combination that equates to a 3" lift.
On our 04 TJ, we run BDS 3" springs and shocks, all 8 Teraflex control arms and rear trackbar, JKS front trackbar, Teraflex TC/tranny/oil pan skids, Teraflex SYE/rear driveshaft, and JKS disconnects.
On our 01 TJ, we run a 4.5" RE Extreme Duty long arm with front Currie Antirock.
We have been very happy with all the components we currently have on our rigs.
I've run components from several different manufacturers. However, we have only run the current generation of Teraflex products--rubber bushings on one end and a Jonny-Joint style flex joint on the other end. I'd have no hesitation running anything Teraflex in the future--although I do like the AEV front steering correction better than the Teraflex front steering correction we have on my wife's rig.