They do so because they want to find a way to earn money and have a better life. It is all about the money not the joy. If they wanted to have fun they would play video games
Video games pretty soon become quite tiresome and boring
I've been there, seen and felt that. Without real interest (read, your money at stake), you will feel exhausted in less than no time. Indeed, I don't mean online games where you can earn things which you could sell for money or which could help you boost your ego. But then they are not particular different from such games as poker and its likes
On the other hand, playing single-player video games or such modes of these games is like rolling dice without risking anything and with no chance to win something actually valuable to you (read, you will quickly lose interest)
Interesting.
So what you're basically saying is that putting something valuable at stake makes a game less boring?
I guess people could play on those kinds of games where useful & unique items can be designed or won by players and sold to other players for money.