Choral groups and musicians travel a lot, leading to the joke:
 
Q: Why do choruses travel so often?
A: Keep assassins guessing.
 
The joke has been cited in print since at least 1997.
     
   
Jeff Bigler’s Home Page
Last modified: 1997/01/03 14:55:50 by .(JavaScript must be enabled to view this email address) 
Chorus Jokes   
Why do high school choruses travel so often?
Keeps assassins guessing.
 
Google Groups: rec.music.makers.choral
Choral Humour
Paul Mestrom
2/8/97
(...)
Why do choruses travel so often? Keep assassins guessing.
     
GuitarLodge.com
bukena
08-17-2007, 11:12 PM
(...)
Why do high school choruses travel so often?
To keep assassins guessing.
     
Google Books
The Mammoth Book of One-Liners
By Geoff Tibballs
London: Constable & Robinson Ltd.
2012
Pg. ?:
Why do sopranos keep touring from city to city?
It keeps assassins guessing.
 
Fark.com
Evilsmurf
2012-01-06 05:19:31 PM
(...)
Why do banjo players tour so much? To keep assassins guessing.
 
Twitter
russlongcore
‏@russlongcore
Why do organists play recitals at so many different venues? To keep assassins guessing. #teamretweet
9:14 AM - 23 Dec 2012
 
Twitter
Kelvin
‏@Cuddly_Biebs
Why do high school choruses travel so far? -To keep assassins guessing.
10:22 AM - 4 Feb 2014
 
Twitter
MusicianHumor
‏@JokesBoutMusic
Why do high school choruses travel so often?
Keeps assassins guessing.
11:09 PM - 13 Mar 2015