Gamifying everday things makes us produce more. If we didn't have a Fitbit counting our steps, we'd probably walk less. If we didn't have people on Instagram liking our photos, we'd probably share less.
We had pedometers prior to Fitbit and Flickr before Instagram but neither of them were set up to optimize rewarding. Now, we can sync our steps to see how we're progressing this week versus last, and compete with friends. We can watch our followers respond to a photo as soon as we post it.
Mobile connectivity drives human gratification. All people want are instant rewards. A step here, a like there, we inculcate the habit by playing for the points.
More about the psychology of digital rewards in here.