A good reason for not setting FIS-style GS sets is that many courses where they have Nastar courses are not large enough to accommodate the gates. Another good reason is that it is recreational - for all comers - and they make a set that anyone can try and have fun with.
A good reason for not having FIS-style GS sets at Nationals is that they set up what, six or eight race courses, and they need room enough to accommodate the courses - and still have regular customers ski. People who show up are at least presumed to be used to skiing a certain style of course and they get a decent facsimile or that at Nationals.
I understand that you may not agree - but I score this discussion at about 10 fer and 1 agin, which might mean something to someone.
Would I complain if they set up a so-called real GS course? No. I would ski it - and see how I did. I don't complain when the course is set on the tight end of the spectrum either. But I can understand why they might set the courses the way they do.
And in any case, skiing is not four separate disciplines - sl, gs, sg, and dh - it is all skiing. Keep your weight forward, initiate the turns, carve if you can, turn high, keep a good line, go as fast as you can without being thrown from the course. Nastar is just another race within the spectrum of race sets.