Actually, you are missing the biggest factor.
Killers have to overpower their victims.
The real sickos need to get them restrained in order to do whatever over a period of time.
In order to keep a weapon produced by the victim from making their day totally the reverse of their intentions they often:
A. Get someone to inebriated to move.
B. Find someone who will get naked ( hard to hide a weapon in a birthday suit)
C. Pick a child or someone disabled.
Prostitutes of either sex fulfill criteria B. Often they can be plied with booze or drugs to meet criteria A. as well. Icing on the cake; since they are living outside the law often nobody misses them.
Deserving it is a lesser factor in their heavy rate of victimization than their vulnerability.
Or D: visiting your hotel during the World’s Fair in Chicago
H.H. Holmes, did he murder 200 people?