Why can't the USA be more like Iceland

That seems to be the desire of the U of Iceland's Thorvaldur Gylfason;

None of the four defects of the US constitution alleged by [Sanford] Levinson (2006) are to be found in the new constitution for Iceland that 2/3 of the voters embraced in a national referendum held by the Icelandic parliament in 2012.

Not that that matters, really;

Even so, the parliament has thus far failed to ratify the new constitution in a blatant attempt to thwart the will of the people, risking Iceland’s standing among democratic nations ...

The world bates its breath. But this is a blatant non-sequitur;

...and reaffirming the importance of Levinson’s point about Congress and the US constitution.

Which is, that Congress doesn't have enough power--it can't easily change the Constitution. Odd, that belief, since Thorvaldur admits, in this article that; The US constitution has proved the most durable written constitution the world has known.... Which would be something to think long and hard about before throwing out the baby with the bathwater.

How likely can it be that a small group of wealthy males, most of them lawyers and several of them slave holders, could have composed a constitution nearly 230 years ago that answers the aspirations of modern society?

We'd say that the proof of the pudding is in the eating, guy.

Can this be part of the reason for the deep distrust that permeates US society at present and for the weakened status of the US in the eyes of its own people as well as on the world stage?

No, we'd say that the people have a healthy distrust of political methods of decision making. That, as one of those wealthy males put it back in the 18th century, Men aren't angels and angels don't rule men. Which is why this criticism is ... bunk;

The first flaw is the blatant violation of ‘one person, one vote’, a core principle of modern democracy as well as a basic human right laid out in modern human rights covenants that prohibit discrimination among individuals in any shape or form.

Which prevents the passions of a temporary mob from easily becoming the law of the land. By design, those wealthy white males didn't want to make it easy for man to exploit man through politics. Considering the situation today in the birthplace of democracy--Greece--they were wise to have done so.

Look around. How is the modern 'one person, one vote' core principal working out in Africa or South America?  In Spain, Catalonia wants to secede. In the UK recently, so did Scotland try. How many governments has Italy had since the end of WWII? (Too many to bother counting, probably about 70)

It's always a good idea for an economist (Gylfason) to ask himself, 'Compared to what?', before recommending a policy change.