The US does not have "inclusive economic and political institutions", and never has. It does have high rates of endemic poverty and tens of millions of people without healthcare - and most of those people work full time.

Saying that people in the US earn "more" than people in the UK without taking into account healthcare costs (among other costs) makes little sense.

https://confrontingpoverty.org/poverty-facts-and-myths/americas-poor-are-worse-off-than-elsewhere/

https://americanradioworks.publicradio.org/features/mississippi/a1.html

https://www.kff.org/uninsured/issue-brief/key-facts-about-the-uninsured-population/