I've never been one to "cat call" but I would imagine guys who do it don't (expect to get lucky) or pick up the woman. They do it because they are immature, consider it to be fun, and they get a kick out of making women blush or cop an attitude. Most guys who cat call usually do it while with friends. In some way they are entertaining each other and making one another laugh while watching a woman's response or lack of. Now naturally if the woman flirts back or appears to enjoy it then of course a guy is going to pursue her. However most of the time it's just guys (saying out loud what they are thinking) when they see a woman they consider to be "hot" or "sexy".