Because it took so much to use your imagination.
Imagine Joe Sixpack, who works at a factory producing widgets all damn day. Some days, he works 10, 12 hours. That's 10-12 hours of using your hands for manual labor so that they don't, oh I dunno, get chopped off by the huge freaking machine right next to you. When you get home from that, you don't have much to use your imagination for. Much less a game that demanded that you use your imagination every two seconds. All that you have energy for is passive entertainment.
I know what a ton of you are thinking. "I use my brain every day, writing complex code... How am I supposed to have that kind'a imagination?"
Meh, it's just different. Writing complex code and having your hand chopped off like Ol' Stubby Joe are two different things. One, you'll get several errors on a computer screen. The other will involve a visit to the emergency room, a significant other crying, and the definite chance that you will die.