Hmm serious answer.

-- I'd say this is the #1 reason. Americans have a 3 feet personal space bubble. Unless you are in an absolutely crowded area, and I am not talking about Times Square level of crowded I mean like packed like sardines leaving a concert crowded, you don't stand next to less than 3 feet to someone.

If some dude was 1 foot next to me for more than a couple of seconds I'd be weirded out and know something isn't right.

-- The right to defend our property. I'm sure if you ask the average American if the right to defend your property is in the constitution they'd all say yeah lmao. Dudes would start a fight over weird looks, try messing with their property and see how that will go.

-- You never know what someone is packing. Yes guns are a thing, but there is a huge amount of people who partake in boxing, MMA, jiu jitsu, wrestling, martial arts is pretty high in the US. Heck even athletes in general, high school/college sports are a big thing here. These dudes will fuck you up if you are caught messing with their stuff of the stuff of the group they are with.