Because they are not the guns of the 80's. Modern auto's are extremely reliable, durable, shootable, fast to reload, fast to fix malfunctions, ergonomic and relatively effective.
The old saying that auto's are more rugged but revolvers are more tolerant of neglect, is mostly not true today. (Not taking a swipe at Chuck, though I did watch the video that Nyeti posted just now) I have seen many, many instances of autos being carried in exposed or concealed holsters, and when they get hauled out once a year for quals, or once every few years, they have all worked just fine for all the rounds in the gun and on the person.
Someone else said that revolvers make better clubs. Not in my experience. I have spent weeks upon weeks hitting people full force with guns, and the autos all came out of it just fine. The revolvers I've seen and tried (not nearly as many as the autos) did not survive as nicely and in many cases, were unshootable afterwards. Same from dropping them on the ground. Usually both types are fine, but I have seen more cylinders seriously damaged and no autos damaged at all. Real world dropping, not testing. I know there are examples of autos failing in these circumstances, but they are extremely rare occurrences.
I could keep going on, but I won't. I love revolvers, and will continue to use them a lot. Let's just not forget how superior autos are these days for serious, professional use. I know no one here has forgotten that, but I felt like typing it anyway. Sue me:-)