The water in some parts of the US has natural chemistry that makes it unpleasant to drink even though it is safe. California urban areas are notorious for this, as an example. In principle you could remediate the water to make it taste good and remove any discoloration (also a thing in a few regions) with enough industrial processing but that would greatly increase the cost of already expensive tap water.

People who grew up in one of these areas are habituated into never drinking the tap water even if they move to a city with excellent tasting and very high quality tap water. I’ve lived in extreme examples of both.

You also see the opposite case, where someone who grew up with amazing tap water naively grabs a glass from the tap in north San Diego and has a “wtf is this” moment.