A brake drum can get stuck in one of two ways. The first way is that you won’t be able to remove the brake drum when you need to change the shoes. The other way a brake drum will get stuck is that it will no longer rotate. The first problem is caused when a lip is formed by braking action on the extreme outer rim of the drum. Normally, the second problem occurs when a piece of the brake hardware either breaks or comes lose, and gets lodged between the drum and the shoes.
For more info, see How to Remove a Brake Drum