I'm not so sure. It seems like it's the design.
My pin lock is pretty much just a threaded bolt that has an extension on the end that a locked cover slides over preventing getting a wrench on one end. This Thule job looks like the bolt threads inside of the hitch leaving no threads exposed with the lock rest jutting out the side. I doubt the threading is uncommon, but the threaded portion on the head end only with the other end the lock rest seems very specific.
At $
18 plus $
6 plus shipping it could be worse.