Exactly general, great points. Enjoying your work is one of the keys to longevity in any career. In sports, fitness and resistance to injury is another obvious key.
Looking at the list again, I noticed there are two representatives in the top 10 in earnings from each sport, except tennis, which has one, and basketball with 3.
Boxing 2 - the top 2.
Football-Soccer - 3 & 4.
Tennis - 5
Basketball - 6, 7, 10
Golf - 8 & 9.
Nobody in the NFL or MLB in the top 10.
Nadal should have been in that list instead of Kobe Bryant at this point. And I think he should be more marketable than the golfers. His fans are legion on facebook and elsewhere. But I checked, and he is
#22 at 32.5 M. 4.5 from tennis earnings and 28 M in endorsements. Back in 2011, his 31.5 M (10.5 from earnings, 21 M from endorsements) was good enough for
#12 on the list. So he's doing better in endorsements and overall earnings, but still slipped compared to the others. I think Rafa's marketing people have some work to do if he is going to get back up there. Novak Djokovic has improved a lot. He is now
#13 with 48.2 M (17.2 M from earnings, 31 M from endorsements).
Oh well, that's life in the fast lane...

Obviously, there are more important things in life. After all, you can only be marketable in sports for so long.
Respectfully,
masterclass