Why is gambling illegal yet the lottery is legal?

I know that gambling is morally wrong. Yes, I know that there are people who literally spend themselves to death gambling. But think of the good that could come out of it. Even though some individuals would bankrupt themselves, the gambling revenue as a whole could be used to build schools, hospitals and neighborhoods. And isn't the lottery technically a form of GAMBLING?? And the lottery has funded some very worthy causes. First of all, why is gambling illegal and second of all, if the lottery is technically a form or gambling then why is it legal?