because it's horribly inconvenient to do it the factory way without a hoist or a very low profile jack.
The subframe mounting points and the front jack points are among the strongest, most stable, and easiest points to hold it up. I usually jack the nose first using the x-member, and place stands under the front side jack points. Then lift the rear with the diff, and use the subframe to body mounts to place the stands. Given the subframe mounting points hold the car up, provide a nice large surface area flat spot to put a good sized chunk of a 4x4 so the stands don't chip the paint and -surprise- also are the actual parts transfering the load of the car when lifting by the diff and the x-member anyhow, why would you consider this so wrong?