“Why is a room full of married people empty?”/“Because there’s not a single person in it.”

A riddle about rooms is:
 
Q: Why is a room full of married people like an empty room?
A: Because there’s not a single person in it.
 
The riddle has been cited in print since at least 1823.
 
         
Google Books
The Nic-nac: Or, Literary Cabinet
Vol. 1
London, UK: Printed and published by T. Wallis, Camden Town
1823
Pg. 72, col. 1:
CONUNDRUMS.
(...)
Why is a room full of married people like an empty room? Because there is not a single person in it.
 
29 July 1835, Schenectady (NY) Cabinet, pg. 1, col. 6:
Why is a room full of Married people like an empty room? Because there is not a Single person in it.
 
1 January 1839, Parley’s Magazine (New York, NY), pg. 68:
Why is an empty room like a room full of married people?
   
Google Books
Riddles, Riddles, Riddles
By Darwin A. Hindman
Mineola, NY: Dover Publications
1997
Pg. 28:
Why is a room packed with married people like an empty room?
ANS: Because there is not a single person in it.
   
Google Books
Teacher’S Joke and Story Book
Collected by Stanley B. Graham
Bloomington, IN: AuthorHouse
2016
Pg. ?:
Q. Why is a room full of married people empty?
A. Because there is not a single person in it?
   
Google Books
Word Games, Riddles and Logic Tests:
Tax Your Brain and Boost Your English
By Adrian Wallwork
Cham, Switzerland: Springer
2017
Pg. 11:
Why is a room packed with married people like an empty room?
Because there is not a single person in it.
 
Reddit—Dad Jokes
Why is a room full of married people empty? (self.dadjokes)
submitted May 4, 2018 by ucom1
Because there is not a single person.
As told by my nine-year-old Keegan T. L.