1. Gambling
I do not refer to a gambling game like pokers, but what I do mention is the gambling system within a game, for example, a lucky draw. Recently, most of the mobile games do require you to draw a random character at the start of your "journey", and the character you draw having different rankings, from 1 star to 5 stars, trash characters to godlike characters. Therefore, the player might have to keep drawing until they got a 5 stars character before they start their game, this kind of system would cause a player to keep restarting the game and this is a kind of addiction.
2. Attractive Story line
Yes, it might cause addiction, because the player would like to know what's going to happen next, so they will keep on playing the game until they see the endings.
3. Arena system
The evilest system in a game, like the MOBA(Multiplayer online battle arena), RTS(Real time Strategy), FPSA(First Person shooting arena) game would always keep the player in the game for their victory, especially for the male player, the instinct of fighting cause them to fear of losing, that's why they will try to keep playing it until they beat their opponents, like LOL (League of Legends), WC3, CS(Counter-Strike), which these games are frequently reported teenager addiction and sudden death in some of the news.
In another point of view, video game addiction is actually a marketing strategy for a game company, because if the player can easily get rid of the game, the game company could have no profit to it. That's why MOBA game is extremely popular and become the mainstream of the industry nowadays and you could see MOBA games in every video game platforms.
Could you blame for the game company? In fact, No. Because the responsibility will eventually back to the