they got 18k out during the ex. They always get a bump. Likely this year the offered something or got lucky. The rest of the season has been the worse attendance they've seen.
Expanding Lamport to 15k would not be a hugely taxing thing and good for the wolf pack.
That though is the real reason I like to think. If the Wolfpack make it through the Super 8s the last thing MLSE, the Argos and the CFL want is to be out drawn by a Rugby team.