When a casino gives their new customer money this is referred to as a no deposit bonus. This was set as a standard many years ago when the casinos first came online. It was the only way they could draw new users into their site to get them to sign up. It became huge and players were talking about it everywhere, sharing on forums letting other knows.
As it grew so did the number of online casinos all competing for the customers which meant they had to match similar offers to other sites. So they too would offer a no deposit specific type of bonus, however it they began to compete more where they would try to outdo the other casinos so some would offer more hoping players would pick them. This pushed up every no deposit casino as they all were trying to get the customers. Then the industry changed where some online casinos started closing down others merge under same ownership and of course they were able to lower the amount they were giving away. The online casinos really do not like the no deposit bonuses but they know they have to offer some as there will always be some casinos giving away money. It is pretty hard to quit a bonus when you set a standard and that is what users expect.
Does the no deposit bonus matter? Really it is all fun but if you’re a player then it really is not a big deal. It might entice you to check the casino out but reality is that the purchase bonus means more anyways. Of course you can have both and many do go for both. The only thing you should look at is if a casino is willing to give you money for nothing then how do you think they will treat you if you become a customer? Normally pretty darn good, other casinos that give nothing will continue to give very little to loyal customers. Just something you should consider.