Why are steering wheels on the left in American cars and on the right in British cars?

It's not really about the cars being "American" or "British", it's about which side of the road they are expected to be driven.

You can find LHD(left hand drive) Jaguars as well as RHD Fords.

The US use right-side traffic, and almost all cars there are built with left-side steering.

England, Scotland, Ireland, Wales use left-side traffic and almost all cars there are built with right-side steering.