National debt and national net worth

I read your article in the Chicago tribune on Sunday, August 22 about the national debt. Thank you very much for an interesting read. I’d like to ask about death versus net worth when we talk about a person we say he has so much debt and so much net worth. So the fact that I have a mortgage on my house is not a problem because my house is worth much more than that. Why don’t we look at the national debt the same way? The US owns many things the capital building the Grand Canyon huge number of vehicles and buildings all over the country doesn’t that count as net worth? Is there a reason why we don’t look at it that way at the national level? We always talk about two things debt to annual income and debt to net worth but when we talk about the federal government we only talk about debt versus income. If you have time I’d very much like to hear about this subject