Liquid soaps are a poor choice from an environmental/cost standpoint. Most of the soap goes down the drain and is wasted. Bar soap stays on your hands and last many times longer.
That may be the case now, but liquid soaps revolutionized laundry when they came to be. Washing clothes with bar soap is a royal pain. Powdered laundry detergents really didn't start to catch on until the 1940's https://en.wikipedia.org/wiki/Laundry_detergent
Also, washing machines didn't really start to catch on until the mid 1940's, prior to that it was still pretty much scrub boards. Scrub boards are bad enough with liquid soap.
I found soap nuts to be the cheapest, most eco-friendly, and reasonably efficient detergent there is. Just drop a bunch of soap nuts in a cloth bag into the washing machine, and it produces enough foam to make everything clean.
Similarly, liquid soap which came to be around the same time.