They are required to ask...even if they see you so often they know you.
When I lived in El Paso I’d go to lunch a lot in Juarez, I’d just walk across the bridge and then walk back.
The same guys would ask, “Are you an American citizen” and I’d say “Si” lol
Then they would ask “Anything to declare” and I’d say “Only my brilliance” (Not my line it’s what Oscar Wilde said when first going through US customs)
This is not about crossing the border.
-—The same guys would ask, “Are you an American citizen” and I’d say “Si”-—
For about a year and a half, I lived in Tucson and worked 3 weeks at a time in southern Sonora. On the way home, I always found it annoying to be stopped at the Border Patrol checkpoint between Nogales and Tucson, since I had just gone through customs at the actual border, so I’d often answer their questions in Spanish for my own amusement.
I wouldn’t refuse to answer, though. At that point, I just wanted to get home.