Nadal is given this award for his fair play, professionalism and integrity; both on and off the court and despite winning it three times, his only other win barring last year was in 2010.
He has won an ATP Award in each of the categories which are voted by players now; these are: Newcomer (2003), Most Improved (2005), Comeback (2013) and Sportsmanship (2010, 2018). He was also named Arthur Ashe Humanitarian of the Year in 2011; and this year he was awarded the ATP Tour No. 1 trophy for a fifth time (2008, 2010, 2013, 2017, 2019).
Roger Federer, Diego Schwartzman and Dominic Thiem are the other players; who were nominated for the award but missed out.
https://twitter.com/rnadalacademy/status/1207772516070154240?s=20