Oh, carbonite freezing isn’t unique anymore. Looks like it is usual business now.
Was it ever implied that it wasn’t unique? All Vader said in ESB was that Cloud City’s facilities were crude, not that anyone had never been frozen that way before. I still don’t know what they usually froze there when Vader wasn’t luring Luke into a trap. 😉
In a galaxy where this technology exists, it’d be weird if smugglers or bounty hunters never realized it could be used to transport prisoners/bounties.
Plus, this show is set roughly 5-6 years after Han was frozen ESB.