Keeping Something In or Out?

Most of the villages have a small cemetery just outside of town. It is easy to spot because it is always surrounded by high stone or brick walls. There will be a gate, locked, often with a cross or saying above.

By looking into this gate, the headstones and memorials can be seen, many with photos and all with plastic flower bouquets.

I wonder why the dearly departed are always stuck inside a tall sealed wall, as if they are inmates in a prison. Especially with some lovely views from the cemeteries' location. Not that the inmate could appreciate the views of course.

Surely spirits could leave by means other than having to scale a wall and so there would be no need to keep them inside and hidden. So is there so much worry about damage done to graves that no one is allowed to go inside? Or that a wall has to be so tall? Would someone really go to the trouble of climbing a small wall to get in? Or destroy an iron fence? Is a 20 foot high wall built to hide everything in the middle of a field really justified? For some reason, I find this very poignant.