Sure. That's all true, but anyone would absoultely leave money on the table for the most part if the promise of things to come was richer with a high degree of certainty. Not Kobe and his situation perhaps, but many other players we are speaking about not at the end of their crumbling career. But you see guys taking less money to win all the time and it leads to playoff bonuses, endorsements from winning, great exposure for your brand and general net worth going up. It's why you see Lebron becoming the biggest name in the world pretty much (took less to win) and guys like Melo hovering where they have always been from a brand perspective.
Regarding your last part - sure, we are talking basketball. Lakers/Kobe is not about basketball, it's about business. We as fans discuss this in the bubble of on court, but owners view it as a business and while winning is important to some/most, business is more important. Kobe while likely killing their basketball/on court chances surely is worth the money when you factor in the business aspect.
We as fans just dont care about that.