Because the weekend is all about luxurious self-indulgence and decadence, Friday day is all about preperation (housecleaning).
But, hmm... the word decadence is from the Latin decadens: to fall, sink, or decay. It's a synonym of deterioration.
Therefore the weekend is all about the path to ruin. Not really the imagery I was going for. Or is it?
The word luxurious also has inherent rotteness it's definition: lecherous. Uh huh. It gets better: lechery is a synonym for lasciviousness. And really, there is nothing wrong with a little bit of its synonym: lust.