Why does the bouncer who sees me all the time always ask for my ID?

I always go to this club/bar all the time and the same bouncer remembers me of who I am because I go tot this club all the time and he still asks for my ID and doesn’t believe that I am old enough to get in. Why is it they still card me? Even when I walk out for a second and come back in, he asks for my ID and doesn’t let me in unless I have it? I would think by now he knows me and knows I am old enough?