I think a lot of the positive sentiments towards the constitution in the 21st century are pretty well linked to its antiquity. While our empire collapses we are drawn to the positive moments of our global reign, the moon landing, World War 2, etc. Americans in general are extremely proud of those moments, and while we enter an unmitigated decline its only natural to look back on them with fondness.
But the constitution seems to hold a special place in American's hearts. It may hold some of that inherent rebellious nature we adore, our anti-colonial heritage that up until around the JFK-LBJ-Nixon years we were very vehement about upholding. Or its just a piece of flawed, but overall impressively forward-thinking, philosophy that can improve human society that's a source of pride.
In either case, its idolatry of a time that passed over a century ago. The beauty of the constitution was its ability to recognize the church's relationship with the state as a major source of social tension and sever that bond to prevent it from destroying our country. It was perfectly executed, and the domino effect of American independence ended the French and, later, British monarchies. However the same villain the church was to a prosperous and civil society is exactly what big business is now. We replaced one monster with another, maybe intentionally. Maybe if we could channel the same ingenuity that the founders had we could fix this issue. But so many people see the constitution as political gospel, where any alterations would corrupt its purity, that we have effectively sabotaged the only method we ever had at using the constitution the way it was intended: To combat whatever new societal evil threatened the well being and freedom of its people.