Gambling is entertainment and like many other forms of entertainment it costs money and can be addictive.
Gambling is entertainment for the gamblers. For the betting institutions it is business and they wouldn't be in this business if it wasn't profitable. The only way it can be profitable is if enough gamblers lose their money. It is that simple. It can be profitable for gamblers as well. But gamblers being gamblers are never satisfied and most will try to win even more which results in heavy losses. For every successful gambler there are at least 100 who fail constantly.