Because it's a normal, common interaction among humans, not particularly charged politically if there's no power relationship between the two people. This guy is not asking for nudes to an intern, for instance.
Public exhibition of sexual desire is acceptable in most contexts. If there's a topic of sexism, it is in the fact that men doing this is more acceptable than women doing it, but this should be addressed by removing the stigma from women doing it rather than adding stigma to men doing it.
But more generally, the policing of celebrities personal behavior to conform to strong social mores is a mostly protestant thing. In other cultures, especially before modernity or globalization, fame allowed you exactly to escape the commonplace social mores because you were outside of the community. Taking celebrities as role models and therefore asking them for moral behavior is a very American thing to do, even though after WW2 this system has been pushed throughout the world.