Why U.S. amphibs omit ski jumps

Why do U.S. amphibious assault ships usually lack ski jumps?

The United States separates carrier aviation from amphibious aviation, so its amphibs preserve helicopter deck space; Britain uses more hybrid ships and gains more from the ski jump.

U.S. fleet carriers already provide CATOBAR fixed-wing aviation, so American amphibious ships can prioritize helicopter spots and well-deck operations; a ski jump consumes deck area needed for that mission. Britain asks its large decks to share carrier and amphibious aviation duties, making the lost helicopter spot worthwhile in exchange for better F-35B launch performance. The different layouts follow different fleet architectures rather than a universal judgment about ski jumps.