One of the huge advantages that online casinos have over their brick-and-mortar cousins in the fact that the size of their casino floor is basically unlimited. Traditional casinos can only offer as many different casino games as their floor space allows, but physical size means nothing in the online world.
Land-based casinos are also very regional, they typically have a certain clientele that expects certain games, and they cater to them online. In Las Vegas you find craps, blackjack, and American roulette; while in Monte Carlo European roulette and baccarat are on offer; and Macao is the home of mah-jong and sic bo. However, online casinos offer casino games to players from around the globe, and therefore offer far more games in one place so that players from Asia, Europe, Australia, and the Americas can still find all their local favourites.
When it comes to slots, online casinos also have the advantage. While in real life, only one player can play a machine at a time, on the internet you can have thousands playing the exact same slot game and the same time. This means that casinos can offer hundreds of different games, because they basically only need one of each. While brick-and-mortar casinos will always thrive due to their excitement and atmosphere, picky gamers that want to find the exact game that they want will find that online casinos are the only ones which can offer them the selection they are searching for.