Those laws are to protect innocent people that might need to be in your home when you're not there. Like police performing a welfare check on people. Man traps are illegal because you can't ensure they only target unlawful intruders. And, most crucially, a trap is intended for cases where you are not present. If you're not present, no threat to your person can exist, only your property.

Man traps and shooting someone in self defense are completely different scenarios. You're only using a firearm to defend yourself if you are physically present and at risk.