Edit: The requirement is explained under https://de.wikipedia.org/wiki/Meldeschein for those who speak German. Basically, hotels and similar operations are required to record the data, mainly to properly apply hotel taxes. Side effect: together with the new registration requirement (you MUST notify that you have moved into a new apartment), and landlords actually being liable if renters don't abide, it makes it extremely hard for wanted persons to live in Germany.