Do we make our beds because of some societal imposition based on some event in history at which time society deemed it appropriate to make beds or do we just do it for neatness?
Making one's bed is a natural activity. Other primates do the same thing each night. While western society has done this for years, the act of making the bed has also been observed in remote, unadulterated cultures as well.
A bed that has been made looks neater to visitors/lovers than a pile of twisted blankets, and it also provides a more welcoming environment in the evening when it's time to sleep. Even the act of making the bed can be therapeutic by bringing order to chaos, venting excess energy/anger by fluffing the pillows, etc.
Don't be lazy! Make your bed!