I had never noticed this before, but I found the following in the help file:
"To rotate cable tray runs in model views, make sure the current display configuration uses a Cable Tray Model display representation for both cable trays and fittings. Only these display representations show an open side to cable trays and fittings, as is necessary to visually represent their rotation."
You need the model representation for MEP space coordination in the 3D modeling world. You can quickly, visually, tell if the duct, waste piping, med gas, and cable trays will all fit above the ceiling.