It serves 2 purposes

1. Further message to the West that this “new variant” is so bad, society must throw everything it has at it, even the mass construction of endless quarantine camps (and, worse, isolation camps). Anything is worth doing if it stops Covid! And just because a few thousand die, and China itself runs out of coffins to send, and doctors are replaced by military squads… it could have been worse!
2. It kills off 10s of thousands of Hong Kongers who have experienced democracy and are thus potential problems for Xi, forever. Plus it makes room for the electric car factories.