Reasons no one goes undefeated at Nationals anymore

1. Kids today just aren't as tough as in the old days.
2. Teams 5-8 are better than they used to be (and 9-16, for that matter). The closeness of the games would seem to bear this out. There were only a handful of games on day 1 where the loser scored less than 10.
3. Teams 1-2 aren't as good as they used to be. It may be that the top players are spread out among more teams. It may have been true that DoG had like 6 of the top 15 or 4 of the top 10 or some such x of y players in the game, but I doubt that any of the teams now is better than 3 of 15 or 2 of 10 (although I'll be damned if I could come up with a reasonable list of the top 15). One reason for this could be that you need seasoning and exposure to become one of these super-elite, after or while you develop your raw skills. In the old days, maybe you needed to be part of a top 4 team to get that exposure, but now, kids get it in college and playing with whore teams and getting plenty of chances to put it on the line.
4. The schedule is hectic, especially compared to the 12 team Nationals up through 1995. Back then, it was 2 games per day, with 90-120 minutes in between. The 14 team schedule cut the break down to an hour between cap and the next round (and I remember that first year that at least one women's game was delayed because the previous game lasted for more than an hour past the cap because they couldn't score in the wind). Especially in the heat, which wasn't a problem in 94, 95, 96, 98, and 99 (and maybe 97, too), it's tough to grind it out for that many in a row.
5. Less importance in winning all your games, since you know that other teams are also going to struggle, and there's no guarantee you're going to get an easy quarters by winning all your pool play games. It's still more likely, but not as much of a certainty as before.
6. Shorter games. It's easier to pull off an upset in a game to 15 (or 13, with the caps) than in one to 19.