No matter what you think, white Americans are mostly German. Here is the top hit when I googled that:

"German-Americans are America’s largest single ethnic group .... In 2013, according to the Census bureau, 46m Americans claimed German ancestry: more than the number who traced their roots to Ireland (33m) or England (25m). "

https://www.economist.com/news/united-states/21642222-americ...

> Here's a list of the top 100 American surnames. The majority of them are British/Scottish/Welsh

Lots of people of other origins adopted English surnames because the British were the dominant early group, and then later people with British names were, even though not always of British descent.

So, now, sure, British surnames are dominant, but that's often not indicative of British descent.

People often adopted English surnames or Anglicized their names, especially around WWI (also when the huge number of German language newspapers mostly closed and even towns named after German places were renamed).