because theres no example in history that has worked better. Its unclear how much of the success of the US should be attributed to the Constitution (what history would have looked like if the US had a canadian constitution for example), but what cant be argued is that the US is the most successful political body in world history and it is the old continuous Constitution in the world.

Under that lense it makes sense that Americans are fairly conservative about changing the constitution and why the founders are so revered. Its just fucking worked out great for us until now. Its really a miracle in many ways.