Trust me, this will happen to you as well.
I can sorta understand it. These guys were stars in their time and getting to around the 10 slam mark was considered something stupendous. Now here comes Federer who wins slams with the same ease as putting socks in the morning. That can't sit well with many of them. Watching Roger, people think Slams are easy peasy but they are actually f***ing hard to win. Look at Murray's problems. Hell, a monster talent like Nastase won just two slams, even though the won the year end championship four times.
Federer's success(who, without Nadal, would easily have 20 slams by now) makes their success, in their own times, seem obsolete and mundane. Remember Borg's 11 and channel slam? Channel Slam has been done and Federer is getting close to 17, 6 more slams. Sampras doesn't really have anything major left over Federer. The rest I won't even into. Only Laver basically has something over Federer.
As I've said on this site Federer is a victim of his own success. He does things too easily, too perfect at times if you will and it makes others efforts seem not that good.