It's really not though.
These three are barely human. As time goes on, people will come even more to appreciate their greatness. it's not that the next generation hasn't challenged them, it's just that these guys are so ridiculously good. Some of the points that Novak had to play in the first couple sets yesterday simply to win points against Nadal was unconscionable.
If Nadal/Novak/Fed played in the 90s, no one else would have a grand slam title except maybe Sampras would have painted enough lines at Wimbledon a year or two to scrape one.