They ain't the only ones that seemingly ain't read it. Open half the postings around here and it becomes pretty appearent that most folks anywhere haven't actually read much beyond the preamble and Bill of Rights.
I don't know about you, but I don't give a damn about other countries constitutions or their thoughts on ours. Has the author really given a look at the other countries in the world? Name one that is better than the US and if you can, go live there.
The problem seems to be, according to them, that our Constitution is relatively free of entitlements. And they think that's a bad thing? Being a "legal backwater" is a good thing - that means the government isn't trying to modify our agreement to take more power from us. "Living document" judges are doing just fine at that already. As for being hard to amend, that's just the way we like it.
Our Constitution is intentionally inflexible on the powers of government. Of course other governments would see this as an undesirable aspect.
That's why ours has managed to survive over 200 years while the average is just 19. We the people haven't granted the government officials permission to draft a new one closer to their liking, so it's taking them centuries to twist and convolute what we have into what authoritarians wish we had.