As a passionate gamer, you probably have asked yourself this question.
(Is it the youtubers, the games themselves, the developers or what?)
In most of popular .io games the player start with weak and powerless level. They can easily be devoured by others. But if they play it safe and smart, it isn’t too hard to process. For instance, in Zombie.io the bigger and longer zombie line pose a larger threat than their newer counterparts. But importantly, the smaller players can take on the larger ones with smart strategies. Starter players in Zombie.io can trick bigger ones bumping into them. So from the perspective of a new player, with little time and effort they too can reach on the top. This is very alluring.
The other thing that makes .io games popular is simple but interesting gameplay. That is to say, there are many possible outcomes in the game as a result of very simple controls and ruleset. In zombie.io all you need to know is that you move with the mouse, avoid bumping into others and make them run into you. Of course there are many other things to know in the game, like using the speed up button to make strategies move. But the important thing is, these information isn’t necessary at the beginning and isn’t even shown to player as a tutorial. Players are left to their own devices and can discover these pieces of information latter. And from these simple mechanics a lot of interesting scenarios pan out.