Eu li sobre https://millionmilesecrets.com/guides/get-a-same-day-walk-in-appointment-at-these-global-entry-enrollment-centers/ (espelho):
It may be hard to get an interview, but some enrollment centers accept walk-ins when you are arriving from an international flight.
Why are walk-ins for Global Entry interview typically only accepted when arriving from an international flight (and not a domestic flight, or simply walk into the airport without taking a flight)?
Adding this now as an answer instead of a comment: The article refers to Enrollment on Arrival as "walk-in". However, the enrollment on arrivals don't happen at the regular enrollment centers, but rather directly at the immigration booths which you only can reach by arriving on an international flight.
Example: In JFK the enrollment center where you can make appointments, is in terminal 4. However, enrollment on arrival is possible in terminals 1, 4, 5, 7 and 8.
Independent of EoA, you can of course just stop by the enrollment center to check if they have capacity for a walk-in (e.g. because of short notice cancellations), and nobody there asks if you had an international flight (source: own experience in February 2019).
To qualify for a walk-in interview, according to the same website you need to arrive from an international flight:
Here is how you qualify for an interview on arrival:
- You must already have received conditional approval
- You must be returning from an international trip
- You’ll need to bring your passport, documents providing evidence of residency: a driver’s license with your current address, mortgage statement, rental payment statement, utility bill and a permanent resident card (if applicable)
That is one of the requirements for a walk-in, although domestic flights are also available for Global Entry:
All Global Entry members are eligible for TSA PreCheck.
But to have a walk-in appointment for some reason you need to be on an international flight.
You can walk in to any Global Entry interview location and hope to get a walk-in interview once you are pre-qualified for Global Entry. (source: I walked in for my interview without a flight instead of waiting a month for my scheduled interview. If they have the capacity or an opening they will conduct your interview then.) The particular mechanism which you are referring to guarantees a walk-in interview, which is why they are hesitant to say that you can get a walk-in anytime by just showing up at the location.