Well, I pretty much agree with the logic here, if the family isn't so well-to-do and doesn't have a lot of money, rejecting such an amount is sheer stupidity, because as you said, beliefs or culture or any other thing won't pay the bills and money is a basic requirement for today's world, you can't do anything at all without it, and if wealth is knocking on your door, you should welcome it with open hands.
The family head which is the fsther have messed up really badly and this shows to a great extent that the father doesn't have love for the son, fine if the boy has gone the extra mile to gamble which may be against most religious mindset but it it we have to understand the impact of this rejection on the physiological well being of the boy.
Now, instead of guiding the son on the way he will spend the money without becoming addicted to gambling and how to make a withdrawal mechanism and reinvest the profits, it will become hard for him to control the boy's actions if he rejects him outrightly.