Dual-national here who has lived in the UK for 17 years, lived in Chicago my whole life before coming here.
Three words: 'employment at will'
In employment at will states, your employer can fire you for absolutely no reason at all as long as it's not discriminatory (age, race, etc). Your employer does not need good cause to fire you.
Also, and this may not be a factor for OP but for anyone who is interested, university costs are WOWZA. Undergrad degrees are four years, not three.
The yearly cost of the university I went to, tuition, room & board etc is currently $78,654. Now multiple that by four.
The culture was (and still is?) insanely competitive about the stupidest things. I have family members who will drive around a mall parking lot for AGES looking for the 'best' parking space rather than just park where there is space because 'look at what a good space I got, suckers'.
Between that and the thought of losing your job for nothing, you're just walking on eggshells all the time.
I won't even get into health insurance and the insanity of having to deal with in-network/out-of-network, negotiating bills, etc. HELLO, YOU'RE SICK! Last thing you want to deal with are staggering bills.