Because Federer is the GOAT. The player all others will be measured by in history, until Nadal replaces him. In 10 years, nobody will care what Nadal's h2h is vs Djok (btw it's still 16-14 Nadal, and 5-3 at slams). Nadal vs Federer rivalry, will be talked about forever. So the bigger lead Nadal can get over Federer, the more glory historically for Nadal. Every Fedal meeting is historical gold for Nadal.
How would I feel if I lost to a player 7 times in a row? The same way Djokovic felt when he lost to Nadal 5 times in a row. 5, 7, it makes no difference.
Honestly i think Fed don't even care about this as much as Nadal. He don't even try to compete like the past nowadays in their matches. Maybe he really think Nadal can't pass him in slams. No more exertion and he hand over the match when Nadal gets physical. Body is more impt to him i think. Unless its indoors and he knows he only need to exercise in short intervals for max 1 hour.
Their matches are not fun to watch anymore cuz Federer kept stopping the rallies(hit to net mostly) when he has a free shot. Its like pointless in his opinion that Nadal will retrieve and he will need to hit the same shot again.