In USA decent food (not full of cr*p and gonna wreck your health) cost, in my experience, twice as much as UK 20 yrs ago, might be 3x now. If you need healthcare, expect big bills, even if you're insured. Many parts of USA you gotta drive everywhere, which is costly. A family might need 2 cars. Seems to me a fair proportion of the larger US salaries get swallowed up. And don't forget you have to work 40 hrs a week vs 37.5 which amounts to 2 weeks extra a year, and Americans generally get 2 weeks vacation vs in UK 4 weeks legal min, often 5 weeks or more. And US employment law is often you can get fired at the drop of a hat. Having no security like that would be called a "contractor" in UK, and compensated accordingly ;)
Look up what American rents are, and you'll see the main cost of living issue.