Yes, the gambling sites are using it to attract people to register and gamble on their sites. This is one of the ways gambling sites can easily get more customers as friends will tell friends to make use of the bonus to bet also.
And of lately this particular promotion by the forum casino advertise here got me thinking too @playgram as they present 100% on first deposit of 30$ so wanted to know if it's limited to a particular slot or applies to all cause my usual slot game that favors me is fruit sweet bonanza 1000
I have not gambled on the site before but other gambling sites that I have used before with this kind of deposit bonus will let it cover all games. I mean you will be able to use it for all any game of your choice. I do not think this would be different on the site also. Also it is just up to $30.