football is the ultimate team sport. no one is going to harp on a cornerback for changing teams. you need almost all of your 52 man roster to win.
In basketball, you only need 7 or 8, and your 1 or 2 main players have a gigantic impact on the game. don't compare the two
not to mention it's a terrible analogy to attribute changing teams with lack of heart. Lack of heart is being one of the most talented guys in your sport but going to another team to defer to another player so you "don't have to be the man". Deion sanders was the man whereever he was going to be. He also performed when it mattered. Lebron has no heart because he CHOKES