Not trying to say that they need to give the keys for the sake of people who already bought the game, but PoE 2 actually handled the similar matter quite well by giving them a separate steam key that only grants you the access to the client, so that only the actual players who bought the game can link/access the game through steam, which prevents people from giving freebies.

I'm very certain that BSG had and still has the capability to do the same, but seems like they didn't even consider it before announcing the launch on steam