That's debatable. What will he clear of that 12m after taxes and deductions (agent, union dues, etc)? 5.5m if he's lucky? He's 24 yrs old. If he lives until he's 85, that's 91k a year to live on. Good, but far from great. Speaking from experience, 90k doesn't go as far as one thinks.
It's not that he left money on the table that make people shake their heads. It's that he A) signed a contract that took him until he's 30 and B) did so for so little. If he'd signed a 3 or even a 4 year deal at 2m per, no one would have batted an eye. He'd be 27/28 and still young enough that if he improved that he would have the option of signing another good contract. Besides, there's nothing stopping him from re-signing in NSH down the road.
This isn't about people being "obsessed with money", but questioning why someone would intentionally handcuff themselves like that. Remember, whatever he makes has to last him the rest of his life. Leaving a few million on the table because he likes things? Again, no one bats an eye. But he's potentially leaving a lot more than a "few million" on the table.