Why are these loops considerably longer than the standard movement?
At these pressures, the VRF flexible loop becomes stiffer than loops operating at the max 200PSI we see in most HVAC systems. The longer legs are engineered to minimize anchor loading.

Why is cold springing recommended?

Cold springing is another way to minimize anchor loads. When the loop moves toward its neutral position, it is imposing no anchor loads.

Why are the loop legs stainless steel and not copper/bronze?
Bronze hose and braid is not strong enough for the pressures.