It could be that there is a mole in the kingdom. In order to make money some wererabit sold the information . So they capture them to work. As for the shifting, maybe their neck as something to do with the shifting so if their necks are bound , they couldn't transform. OR maybe if they transform,they would choke since the collars are tiny. As for the collar maybe it is made of steel.
The company might stole alot of wererabit or have a small amount of consumers
I can come up with a ton of excuses to make this make sense, but it's not the point I'm making.
And even if it's made of steel, they have to actually close it somehow. Unless they soldiered it closed (though that would severely injure the wearer, so it's not an option), there should be a way to get it off, especially off a rabbit, that's not too difficult
I'm sorry, but this wererabbit slavery plot twist is sooooo bad. There are so many things that don't add up. How did they just conveniently develop collars that prevent shifting that are impossible to get off again. How did they find out these rabbits are good at making medicine. How is this an actual functional business? It just all seems so goofy and stupid now. If Neungso's brother had sold them out to a lab doing experiments or something I could've gone with it, bus this is just silly.