In many countries hotels are required by law to keep passport numbers of foreign guests. In the US there is, apparently, no federal law; however, it is often p

In many countries hotels are required by law to keep passport numbers of foreign guests. In the US there is, apparently, no federal law; however, it is often part of state law: https://travel.stackexchange.com/questions/76012/laws-requiring-identification-at-hotel-check-in https://travel.stackexchange.com/questions/76012/laws-requir... In many more countries hotels do it despite it not being required; they just do it to assist law enforcement agencies. And doubtless they like to keep the data themselves as an effective way to track and mine guests across multiple visits.