The relatively low US death toll can be attributed to a number of factors. Firstly, the US troops landed on beaches that were less heavily defended than those that the British and Canadians landed on. Secondly, the US troops had more air and naval support than the British and Canadians. Thirdly, the US troops were better trained and equipped than the British and Canadians.
Overall, the US death toll on D-Day was relatively low compared to the other Allied nations involved in the operation.