I of course can't speak for everyone, but where I live, all municipal water is safe for drinking. It seems many people (including my wife) think that if water doesn't come out of a plastic bottle it's not good to drink. I even have a seven stage RO system at home that feeds my refrigerators and ice makers always with less than 5ppm TDS and multiple carbon taste and oder filters on the outlet of the RO membranes, and my wife still buys bottled water!!! I have shown her tests of the bottled water versus our water and even my spot free water at the carwash, both have less TDS than the bottled water, to no avail. I still drink out of the garden hose if I am hot and working outside during the summer.
I guess your answer is many people in the US are spoiled and believe if it's not bottled, it not good.