The biggest advantages of playing at new online casinos are new games and new bonus mechanisms. When you play at a new online casino, you can have bigger and greater access to the game based of the casino compared to other established ones. More than that,  the bonus system is very innovative with many reloads and a more attractive welcome bonus with a decent wagering requirement.
New online casinos attempt to do that because they know that they need to attract more and more players and keep them playing at the sites.