So that you don't have to shop alongside the peasants buying Chevys.
Members of the public don't generally get to see them, but dealerships are given long lists by manufactures of things they are required to do or offer in order to be able to sell a given brand of car. For some luxury brands, this means an entirely separate area for their cars, and the extent to which they need to be separated will often depend on how expensive the cars are. But Cadillac has recognized the value of this kind of exclusivity, and is going to start moving toward this model.
The exact specifics haven't been detailed, but essentially, Cadillac would like to offer a "boutique" shopping experience with better trained sales staffs, more luxury amenities and a more personalized experience. This is going to be a very expensive undertaking for dealerships, and we're guessing that it won't be a requirement for dealerships in order to carry the brand, but rather that Cadillac will offer special incentives and rewards for those dealerships which do endeavor to follow whatever these new guidelines will be.