There are more than 200,000 slot machines in Las Vegas. They are popular because players don't need any gambling knowledge and slots require only a very small bet. They make money by paying out less than they take in. Slots account for more revenue to a casino than all other gambling games combined. (The state of Nevada collects a $250 annual tax plus a $20 quarterly license fee per slot machine plus a percentage - about 5% - of gaming revenue.)
and billions of dollars in tax revenue to the state. The reason is that they provide the most profit to a casino. It is not accidental that two-thirds of every casino is littered with row-upon-row of slot machines of every type imaginable.