Circumcision removes a lot of the sensitive tissue, making it harder for a man to climax, especially while masturbating.

It’s done primarily by religious loons to ‘keep men from committing sin’, since they believe the only way a man should ever climax is during penetrative sex with a woman. But even then a circumcised man will feel less pleasure than an uncircumcised one.

So this is primarily done to get some of the feeling back, both to be able to masturbate easier and to have greater pleasure during sex.