Why is it that when I travel to certain places I need to ensure my passport has at least n months before it expires? So what if it's due to expire next week if I'm only staying until next week. Even if I'm staying 2 weeks and it expires tomorrow, why does that matter? I guess I might not be allowed back into my home country, but that should be my concern, not the worry of the immigration of the country I am going to.
What kind of illegal immigration / criminal activity does a country prevent, or economic benefit / any other advantage does a country get by enforcing this kind of rule?