I am wondering why the first well known example of non-tempered irreducible admissible representation of $p$-adic group $U(n)$ should be $U(3)$. Because, Gelbart and Rogawski suggested the non-tempered representation of $U(3)$ using the theta lift.

I know all irreducible representation of $U(1)$ should be tempered because $U(1)$ is compact. But why isn't there known example for the non-tempered representation of $U(2)$? I think it should be there.