I would think most peoples' preference (absent pressure from management) is to, in this order:

1) stay home, dick around (or do laundry, play with children, whatever)

2) dick around at the office (ping pong, fancy beer, etc.)

3) stay home, get work done

4) get work done in the office

Under mandatory office attendance, you are only really allowed to choose between 2 and 4, so naturally more people will choose 2. Under optional attendance, all choices are available, so more people will choose 1