Beginners might learn vim to modify their ~/.i3/config, hex values for coloring their desktop, or basic CLI commands to add functionality to their keybindings. Maybe they want to add a customized weather applet to the bar at the bottom of the screen, so they write a shell script utilizing wget. Soon enough they're learning to install Arch Linux (because everybody else on that "Show off your desktop" thread is using it), and it's not long before they're a full-blown linux fanboy. That's at least the route I took.
It's not that i3 is popular among these communities because it's the easiest, but because it looks the coolest and offers the most amount of visual customization. But after getting used to it, there's an incredible amount of depth and usability that keeps you on it. I really can't imagine a more effective window manager.
If you're looking for neat-looking i3 setups, check out reddit.com/r/unixporn/ . If you're interested in getting started with it, somebody made a great tutorial for it at youtube.com/watch?v=j1I63wGcvU4 .