And why should it be?
Here in Virginia, I can legally take a loaded pistol right into the General Assembly chambers or even the Governor's office. What makes the Congress so special. They have convinced even conservatives that they deserve special protections. Granted, with the shenanigans they pull all the time, they might have reason to be. But they have insulated themselves so much from the citizenry that they have little to fear.
So you have no problem with someone carrying a loaded gun into the Congress? What about the White House? What about an AKA-47?
They are not getting special privileges. You can't carry a loaded gun into my office.