The primary reason that I am a 3-rail runner is that I can run large engines in a relatively small space. The minimum curve on both my home and club layouts is O-72. I can run any 3-rail engine on these curves. Many, if not most, 3-rail layout builders on the forum run on curves smaller than O-72.
I believe that if 2-rail models were designed to negotiate O-72 curves and had the same detail level as Lionel Legacy or MTH Premier, then the 2-rail segment would take off. The biggest reason that 2-rail remains a small hobby segment is that the large curves require too much space. NH Joe