So soap got less and less effective for all its cleaning uses. I guess the water was always pretty alkaline in some places, so soap was never an ideal cleaner. Around the beginning of the twentieth century, household detergents became available. Detergents have no problem with alkaline water, so they were really popular. They soon became cheaper than soap, too.
Detergents are excellent cleaners for most uses.
I moved recently, and suddenly started having problems using soap in my hair. The problem is that hair reacts to acids and alkalis. Acid makes the scales lie down flat, which makes your hair shiny and smooth. Alkali makes the scales stand up, which makes your hair look dull and feel rough and tangly. Therefore hard water, which is common these days, makes it harder to wash your hair.