Anyone know how celebritys visit our soldiers overseas? why don't they become soldiers and live with them too?

if they became soldiers themselves wouldn't that help spike morale? instead of visiting them they could create a constant presence, show them that they are supported by someone that they would normally ask for an autograph. Why don't the celebritys become soldiers instead of visiting them. To actually know why they should be thankful instead of being thankful for the cameras. Tell me why none of them has become a soldier in support of the soldiers that have supported us from even before some of us were born.