The problem with passports in the US is that they are not particularly common forms of ID so folks like liquor store clerks, bartenders etc. requiring proof of age are unfamiliar with them, preferring the "traditional" driver's licence or state-issued non-driver ID card. Passports are also physically large items to carry about in daily life compared to the credit-card sized DL and they are difficult and expensive to replace if stolen, lost or damaged beyond use (I'm just back in Britain from Japan where the tourist information service warms visitors to Nara and Miyajima tha the tame deer in those locations will destroy papers such as passports in their attempts to mooch food).