As I see it, there are three or four reasons a player keeps playing:
- To win (and/or break records)
- For love of playing
- Money
- To stay away from home/wife/family (e.g., Tom Brady)
Hard to know what factors are at play for Rafa. He's always been a humble guy, though obviously he wanted to catch Federer in the rankings back in the day, and more recently the Slams. He can retire knowing he surpassed Roger's Slam count, but has to realistically feel that Novak will be harder to keep ahead of.
Could it be love of playing? I think for Rafa 1 and 2 go hand in hand. Again, he seems less driven by records than Novak or even Roger, but he'll only love playing as long as he feels like he can win at Slams. Meaning, he loves playing to win.
I don't think money is a factor - he's got plenty. As for the 4th, who knows how he's taking to being a dad. For some it is hard, especially at first, because all of a sudden you become #2 to your wife, plus all the dirty diapers, crying, etc. For all it changes your life. In fact, this is another factor: When a man procreates, it softens the testosterone-driven urge to win/conquer. Being a father is more remarkable and magical than any tennis accomplishment, or at least deeper and more long-lasting. He seems like the type of guy who could really settle into it. I can really imagine him casting fishing rods with his son or daughter in the Mediterranean...