The only two serious injuries I can recall are when he hurt his back in a Wimbledon semi-final against Raonic and that was when Murray went on to win the tournament - back in 2016. He had an operation on his knee and then returned to action but skipped several tournaments to recover until Wimbledon but he already had back surgery by then.
During the same period Nadal was suffering from an injury, both players were injured and not playing tennis while they recovered from injuries but met up for the launch of the Nadal Tennis Academy in Spain just months before the 2017 Australian Open and neither would have believed that the two of them would be in the final. I think that 5 set final in 2017 that Federer won was one of the most exciting tennis matches I ever saw. That fifth set that Nadal was leading 3-1 in the final set but had his serve broken twice by Federer and when he won Federer became the first man to win at least five singles titles at three different Grand Slam tournaments.
You are right though, apart from that period in 2016 and also early this year Federer has been almost free from injury throughout his life, probably thanks to a genetic make-up from sports playing parents. Nadal has been suffering from foot and knee issues all his professional career and Djokovic has had elbow and other issues too.
It is just a statistic because at Grand Slams it also something that people factor in because it is the only tennis tournament that has a winner based on the first to win three sets (best of 5 sets).
In fact Federer reached a record 36 consecutive Grand Slam quarter-finals between 2004 Wimbledon and 2013 Roland Garros. That is a record unmatched and will probably never be broken.
Also Federer has won an a record 20 Grand Slam singles titles (joint with Nadal) and a record 31 Grand Slam finals (10 consecutive, and another 8 consecutive – the two longest streaks in history), 46 semi-finals and 57 quarter-final appearances and with them being the best of 3 sets they are always going to be factored in and really classed as irrelevant.
but that means he had a lot of lost matches. the fact that someone has the highest number of lost finals can't help them to be promoted as greatest of all time. Rodger is older than Novak and Rafa, so he played a little bit more Grand Slam tournaments, it is not insignificant facts.
Of course, it can be ignored his constantly high level of quality for years. Plus little luck with injuries, I can't remember when Rodger had a long break due to injury.