Basically it makes people feel good. Growth is exciting and motivates people to do stuff. Shrinkage makes people sad, depressed and more likely to try to protect what they have. It's often irrational, but that's just the way it is.

Growth isn't sustainable, of course. If you're a gardener you get to experience the joy of growth every year, but you have to "pay it back" in autumn and winter as everything dies back and resets. The seasons force it on you in the garden, but we can't force it on ourselves. We'll just keep having summer after summer until it all goes boom.