I am not knocking the US but I really don't count domestic trips since I do so many of them. I was a pilot for 33 years and saw a lot of the US from the air and spent lots of time on the ground between flights. Additionally, we did a lot of wilderness travel by canoe, horse or even foot. I have probably seen 90% or more of the US park system.
I mean all I have to do for US or Canadian travel is jump in my truck, add gas and go. And honestly traveling in Mexico only involves about 30 minutes at the border doing Customs paperwork which is then good for 180 days.
So, I don't think I have missed much in my own backyard but am wondering what is over the fence and on the other side which may be worth seeing.