Each year for many years, I frequently enter the US with foreign visitors who are VWP nationals. It is rare that my visitors are asked for a printed itinerary unless the airline and/or CBP thinks they are a one-way itinerary; and even then, it is rare for the CBP to ask them for a printed itinerary on arrival in the US or at a US CBP pre-clearance facility.

The last time an immigration type asked me for an itinerary when entering a foreign country without a visa was when traveling into the UK at LHR. There and elsewhere, it's more typically the younger, female and/or ethnic minority passport control types in the US/Canada/UK/Australia/New Zealand that seem to make more of a stink about itineraries when I'm part of the travel party.

Most of my VWP national visitors make their trips to the US with a smartphone with their ticket details and their passport. Printed itinerary or even printed ESTA clearance not required for them to travel to and enter the US.