How does it keep the same spring rate but become soft? isnt spring rate whether its soft or hard or am i missing something?
That was a little poorly worded. A standard spring is designed for a relatively large amount of travel. For example, at the original ride height the car may be able to travel 200mm before hitting the bumpstops. Once lowered, the car can no longer travel this far before hitting the bumpstops, it may be reduced to something like 150mm of travel with a 50mm drop. If you compress the springs you still have the original springrate, which will likely be too soft with the vehicles new ride height.
Choice makes sense to me now