The US has a huge internal market, with free interstate trade and no need for localization.

The US has accumulated colossal scientific and R&D resources, which regularly produce industrial breakthroughs. Lower taxes help, too. (Lower taxes is what a country can afford for general benefit, not a sloppy pro-rich policy.)

But most importantly, USD is effectively the world's reserve currency, so the US can literally print money, and much of the rest of the world would gladly take it; it's like gold, only buttressed by the US's economic and military might.

The UK has none of these advantages. The British Empire had some of these, but it's gone. Another large factor is that the US emerged from WWII relatively unscathed, while Britain was badly hit, and could not grow as fast.

(Edit: typos.)