Because vaccinated people mostly don't believe they're immune. We believe we have a strong protection against infection and a stronger protection against death, but that doesn't mean immunity.
My wife and I have been fully vaccinated since May, but we've had several tests since then (so far all negative) when we learned about contact with infected people or were experiencing suspicious symptoms.
My wife and I have been fully vaccinated since May, but we've had several tests since then (so far all negative) when we learned about contact with infected people or were experiencing suspicious symptoms.