And ~80% of that lives on the ~20% of land in Europe, making the rest of Russia very sparsely populated.

Also the US has five times the population of the UK, and 40 times the area.

And its not like the UK has a uniform population density internally - we have a greater area of peat bogs than built up areas:

https://www.sheffield.ac.uk/news/nr/land-cover-atlas-uk-1.74...

And a lot of the US is pretty sparsely populated.