Why U.S. Marines were absent from Normandy

Why was no U.S. Marine division used in the initial Normandy landings?

The Marines were committed in the Pacific, and the U.S. Army had already built substantial amphibious experience in North Africa, Sicily, Italy, and the Pacific.

The U.S. Marines were heavily committed in the Pacific, with a division of responsibilities between theatres. By Normandy, the U.S. Army had participated in Torch, Husky, and landings in Italy, as well as amphibious operations in the Pacific. Those campaigns gave it substantial landing experience. The absence of a Marine division therefore does not mean the initial Normandy assault lacked an experienced American amphibious force.