And many people buy bottled water to drink at home, where there is tap water available. That's the choice they're talking about, not you choosing not to use the non-existant faucet in your car.
Sure, but it's not a uniquely American thing. Lots of people in Germany buy bottled water to drink at home, and Germany's tap water is perfectly fine, under constant quality control, there are countless rules against pollution, tap water has to comply with stricter regulations than bottled water and therefore often is of higher quality etc etc, and has been for decades. Still, people buy bottled water.
My in-laws’ delicious tap water is from the Harz Mountains, and yet, they insist on serving a rather sulfuric, somewhat-carbonated bottled water. They have trouble believing that no, I honestly prefer their tap water.