More water is only a feature if you’re using stone age detergents. Modern detergents don’t benefit from more water, but they do benefit from better agitation.
Modern detergents use enzymes to break down dirt and material to bonds dirt to your clothes (like oils and fats), they need good agitation to physically separate the loosened material, where surfactants in the detergent can then bond to dirt and keep it suspended in the water. They’re so good, at keeping dirt in the water, that you just need enough water to saturate the clothes, and form a small amount of cleaning liquor. A drain and rinse cycle then completely removes the dirt from your clothes.
Adding more water makes the agitation far less efficient, because rather than being able to pick up and drop your clothes on to other clothes, or the hard surface of the wash drum, your clothes hit water first which cushions the impact. Resulting is less effective removal of dirt.
Finally modern detergents work best with plenty of time. The enzymes doing the heavy lifting don’t get consumed in the process, so the longer they’re in contact with your clothes, the more dirt they can break down. (Also worth mentioning enzymatic cleaners don’t damage most fabrics at all, because they’re carefully designed to only target dirt)