There are different types of sweepstakes. Not all of them come in the category of lottery or gambling. If a sweepstakes is merely promotional where no purchase is necessary, then it is like a prize or award that the business volunteers to advertise its products and to attract more customers. Such sweepstakes are permissible in Islam. But if a sweepstake requires to purchase a ticket or something similar, and get nothing in return for the value except for those who win, then it would be Haram, because that would be gambling.
Lotteries are, perhaps, the most widespread form of gambling.
In most lotteries, the gamblers buy numbered tickets. In many State lotteries in America the chances of winning are one to fourteen million times. It is deceitful. It lives and thrives by consuming the hard-earned resources of losers. It depends on the losses of many.