Why are they called sleepovers when no one actually sleeps?

We had our niece sleep over last night which at first seemed like a great idea but Ruby felt otherwise when it was time for bed. I let them stay up late (AKA 8:30pm) and then brought them up to brush teeth and go to bed. Ruby starts to scream. SCREAM, just the way she does when we are out in public and she "is afraid of all these people." I take Kaylee back downstairs with me and let Ru hyperventilate for a while. After about 15 minutes I bring Kaylee back up and they are FINE. But then they stayed up until 10pm. This is the super condensed version because I found the entire event to be too annoying to give you the entire re-play. I am not in a hurry for sleepver #2, not in the least...