If it’s hardwired in, it’s not significantly harder to steal than otherwise. Clipping a couple of wires connected to a doorbell transformer is significantly easier than dealing with whatever mechanism is used to release the doorbell from it’s attachment.

Also, you would be stealing a camera that will film it’s own theft and upload the footage on it’s way out.

Additionally, these devices aren’t exactly expensive anymore, not a whole lot of value in stealing them. Even if stolen, not a huge setback to buy another one.