That’s not true. US citizens maintain their constitutional rights at the border. That has been tested in court. This is not the case for non-US person.
Also note that Miranda rights are not constitutional rights.
This guy requested not to proceed without his lawyer present several times, with no result.
It seems to be more true than it did a couple of decades ago, what with more recent rulings like US v. Cotterman and US. v. Koluz better clarifying what counts as a routine border searches vs. more in-depth "forensic" searches that require individual suspicion.
you'll find it's the same people