Work, commuting, romance or kids take up so much time and energy that it is so much easier to crash on your couch and lose yourself in mindless activities.
Now if you think about it, you probably have zero interest in people who you find mean and ugly, meaning your pool of potential mates gets a bit smaller.
It is no use inviting the politician or the professional or business man, who has been working or worrying about serious things for six days, to work or worry about trifling things at the weekend.