Just because they don't bother finding you doesn't alter the fact that they are supposed to.
Besides remember what the Americans did to John Walker when he 'apostated' from the Americans side? They didn't kill him they tortured him and shamed him publicly by shaving off his beard and so on to set an example to anyone else.
When someone joins the army, they sign a contract in which they are fully aware of the consequences of apostating. By accepting Islam you are making a contract with God. If you accept Islam as the truth you are under obligation to live by its laws. So you see Bro it's the persons own fault and a religious contract is much stronger than a man-made one.