This is the single most important factor of all. You want to have a good time; you have money; you spend it in a way that you enjoy. This is by far the most common reason for non-problem gamblers to gamble. Casinos are places of entertainment, no different from amusement parks and movie theatres. When you go to the casino primarily to enjoy yourself, you're gambling for a good reason.
Many casinos have created vast opportunities for their local communities through hiring of employees, contracting with local businesses, and drawing in large numbers of people who stay overnight at local hotels. So while most of those people may go home losers, they will have injected new wealth into the local communities.