CBP could ask who a visitor is staying with. Furthermore, CBP has discretion to contact said individual if they suspect anything at POE. And if they gleam anything suspicious about the host, CBP could set in motion scrutiny of the host.
Hypothetically (not tying anything to OP), what if a visitor unknowingly gets associated with a name/address of someone involved with, say drugs/prostitution, etc and that triggers a CBP alert? Doesn't always happen, but ya never know.