I don't agree with most of the reasons stated in this thread, but then again, I don't believe it is impossible to build a modern course as good as Pine Valley. To me, Sand Hills is just as good as Pine Valley, and I have worked on a handful of courses which were pretty close.
No modern course can compete with the legend of George Crump and 90 years of history, so it may well be that no modern course can knock Pine Valley from its consensus #1 ranking. But that's because of the politics of rankings, not because golf architects aren't creative enough, and certainly not because we can't build as good with modern equipment. On the contrary, in the right hands and allowing enough patience, we can build things today that George Crump could not have. We just can't get the same 90 years of mature vegetation that Pine Valley now has for opening day of our new designs.
It is also true that very few clients would have the nerve to build something as severe and demanding as Pine Valley, because they are afraid it would make it too difficult to recruit a full membership roster. Most of today's best developers (including Mike Keiser and Mark Parsinen) just aren't that sort of player, so they would not build such a course. Mr Crump's one great advantage was that as developer and architect, he did not have to seek approval from anyone. That would be a rare circumstance in the modern era, but it's not impossible ... It would just take a lot of guts.