I played video games (90s super nintendo) when I was a kid primarily for the music/artwork. Then the internet came along where I could enjoy the art without hitching my time to a game. With my time unencumbered, it wasn't hard to discover that reality is a better game with better music.
I guess what I'm curious of is this: What do games offer these people that reality doesn't? I'm not talking about people who play casually here and there, but rather people who spend well over twenty hours per week playing games, sometimes longer.
I'm sure there are some professional MMORPG players out there fuming right now, thinking, "I made XXX dollars selling equipment on ebay." or "I made XXX dollars winning such and such tournament." Porn stars also make a lot of money.
If I had to make a wild guess as to why people stay on the smack into adulthood, it would be escapism. When life paints you into a corner, it is very easy to retreat into the virtual world with netflix and xbox. Urban Japan is hard mode, so probably a much higher percentage of people being painted into corners. Still probably better than netflix though. At least it's an active pursuit rather than a passive one.