Federer's losses/struggles are attributed to sickness/decline/mono/Mirka's nail appointments, etc.
Nadal and Djokovic's losses/struggles are exclusively attributed to being outplayed.
Is that explicit enough?
What forum have you been reading?
Nadal's struggles have been put down to getting out of a chair, having a lack of 'illusion', being tired after the SF (almost every time Federer beats him in a final this comes up), bad knees, bad foot, bad thumb, foot blisters, parents' divorce.
Nole's list is way longer, including contact lenses, and he didn't like the flowers at the Australian Open
Too much pollen for the Spartan.