1. There are women that DO respond to that approach . . . therfore it is rewarded and repeated.
2. Women that don't respond to the approach RARELY give the men shit about it . . . Therefore there is no negative feedback and behavior continues. Got to to take my hat off to you for responding that way.
3. When men whistle catcall whatever, they are just showing appreciation for your looks. ITs really not a bad thing. I have had girls driving by whistle, beep, shout, etc. I kind of liked it