The whole point is LeBron taking way less money. What I meant by needless money was that LeBron and those stars already have so much money that more wouldn't help them much. I know it's a weird concept but think about it.
You've figured out the secret! No, actually there's a reason why it doesn't happen in professional sports. It's a business and players are trying to make as much money as possible while they can. When a player does take a discount it's usually only a slight one, or it's close to the end of their career when they probably should be making less anyway due to a pending decline in skills.
What you should be thinking is a "weird concept" is the entire notion of a salary cap and max salary limits in what is supposedly a free capitalist country. Why should players take less (making the owners happy) when their salaries are already artificially constricted? How do you decide which player takes less and which makes more? Why should LeBron, or any other superstar who is worth more than the max, take a massive pay cut so they can sign someone else less talented to a higher contract? Doesn't that strike you as "weird"?
Consider that these stars are already underpaid their first four years in the league due to the rookie wage scale. How much money did LeBron make for the league his first four years while he was stuck on a rookie deal? Shouldn't he have a right to make that money back?
Also, endorsements are only lucrative for a handful of top players. The other lesser stars still make most of their money from their contracts.